How to Display a Local Base64 PNG in a Handlebars Puppeteer PDF

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Read the PNG on the Node.js side, convert its bytes to Base64, build a data:image/png;base64,... URI, render that URI through Handlebars, and pass the resulting HTML to Puppeteer. Chromium cannot resolve a server-side filesystem path from page markup, but it can render an image whose bytes are embedded in the HTML. After the page loads, call page.pdf() to create the PDF.

The complete pattern

The safest general flow is:

1. Read the local file with Node.js fs.
2. Encode the bytes with buffer.toString('base64').
3. Keep the fixed data-URI prefix in the Handlebars template and interpolate the Base64 payload.
4. Compile the template and call page.setContent().
5. Wait for the image to complete, then call page.pdf().

This keeps the image self-contained in the HTML sent to Chromium. Do not put a Node-only path such as /srv/reports/logo.png in an <img> tag and expect the browser page to read it.

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Runnable Node.js example

Install the dependencies

npm install handlebars puppeteer

Save this as make-pdf.js. Replace the example path with an absolute path to your PNG.

const fs = require('node:fs/promises');
const Handlebars = require('handlebars');
const puppeteer = require('puppeteer');

async function makePdf() {
  const imageBytes = await fs.readFile('/absolute/path/to/image.png');
  const imageBase64 = imageBytes.toString('base64');

  const template = Handlebars.compile(`
    <!doctype html>
    <html>
      <head>
        <meta charset="utf-8">
        <style>
          @page { size: A4; margin: 18mm; }
          body { font-family: Arial, sans-serif; }
          img { display: block; max-width: 100%; height: auto; }
          h1 { margin: 0 0 12px; }
        </style>
      </head>
      <body>
        <h1>Report</h1>
        <img src="data:image/png;base64,{{imageBase64}}" alt="Report image">
      </body>
    </html>
  `);

  const html = template({ imageBase64 });
  const browser = await puppeteer.launch();
  try {
    const page = await browser.newPage();
    await page.setContent(html, { waitUntil: 'load' });
    await page.evaluate(async () => {
      const images = Array.from(document.images);
      await Promise.all(images.map((image) => image.complete
        ? Promise.resolve()
        : new Promise((resolve) => {
            image.addEventListener('load', resolve, { once: true });
            image.addEventListener('error', resolve, { once: true });
          })));
    });
    const pdf = await page.pdf({
      format: 'A4',
      printBackground: true,
      preferCSSPageSize: true
    });
    await fs.writeFile('report.pdf', pdf);
  } finally {
    await browser.close();
  }
}

makePdf().catch((error) => {
  console.error(error);
  process.exitCode = 1;
});

The page.setContent() call assigns the generated markup to the page. page.pdf() then generates a PDF using print CSS by default. The explicit image wait is useful when the document later contains additional asynchronous image processing; for a simple data URI, the image is normally available immediately.

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Use a different image format correctly

The MIME prefix must match the bytes. For a JPEG, use data:image/jpeg;base64,; for WebP, use data:image/webp;base64,. Do not label arbitrary bytes as PNG. If uploads are untrusted, validate the detected file type and impose a size limit on the server rather than trusting the filename or a caller-supplied MIME label.

Handlebars escaping and data-URI construction

Handlebars HTML-escapes ordinary {{expression}} interpolation. A robust template keeps the fixed markup and prefix in the template and inserts only the Base64 payload:

<img src="data:image/png;base64,{{imageBase64}}" alt="Report image">

After rendering, inspect the HTML during debugging and confirm that the value starts with data:image/png;base64, and contains the expected payload. Base64 normally contains letters, digits, +, /, and =; ordinary interpolation remains the safer default.

You can instead construct a complete URI and use triple-stash syntax, for example <img src="{{{imageDataUri}}}">. Triple-stash emits raw output and disables normal escaping. Use it only when the value has been generated and validated for this exact attribute context. Never pass untrusted text through triple-stash or mark arbitrary input as a Handlebars SafeString.

Validate before rendering

For a production upload pipeline, check the first bytes (the PNG signature is part of the file format), reject unexpectedly large files, and decode or inspect the image with a trusted image library when your threat model requires it. A filename ending in .png is not proof that the content is a PNG.

Control print layout and colors

Puppeteer uses print CSS media for page.pdf(). If your report is designed with screen styles, select screen media before creating the PDF:

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await page.emulateMediaType('screen');
const pdf = await page.pdf({ printBackground: true, format: 'A4' });

When you need print styles, omit emulateMediaType('screen'). Background colors and images are not printed unless you request them with printBackground: true. Chromium may adjust printed colors; CSS using -webkit-print-color-adjust can request more exact color rendering, but the final result still depends on the installed Chromium build.

Use PDF options such as format, margin, landscape orientation, header and footer templates, and page ranges according to the Puppeteer version installed in your project. The API surface and defaults can change, so keep the Puppeteer package version controlled and check its matching API documentation when upgrading.

Size the image deliberately

max-width: 100%; height: auto; preserves the PNG’s aspect ratio while preventing it from overflowing the printable area. If the source is very large, resize it before embedding or constrain its CSS dimensions. Base64 adds approximately one third to the encoded byte representation, and the complete HTML must remain in memory while Handlebars and Chromium process it.

Images in headers and footers

A data URI is a reasonable approach to try in a PDF header or footer. A Puppeteer maintainer wrote in a 2018 issue that “the base64-encoded image should work just fine,” but that statement is historical rather than a guarantee for every current release.

A separate issue opened on April 3, 2025 reports a Base64 header-image failure beginning with Puppeteer 24.4.0. Treat that as a version-specific user report, not proof that all later versions fail. If a logo appears in ordinary page content but disappears from a header or footer, check the exact Puppeteer and Chromium versions and inspect the final header-template HTML in that environment. When the layout allows it, put the logo in the main document body; that avoids special header/footer rendering behavior.

Example header template

const headerTemplate = `
  <div style="font-size:9px;width:100%;text-align:center;">
    <img src="data:image/png;base64,${imageBase64}" style="height:18px">
  </div>`;

const pdf = await page.pdf({
  format: 'A4',
  displayHeaderFooter: true,
  headerTemplate,
  footerTemplate: '<div></div>',
  margin: { top: '25mm', bottom: '20mm' }
});

Give the header enough top margin or it may overlap the body. Test this path against the version you deploy rather than assuming behavior from an older issue or a different Chromium binary.

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Choosing the image source strategy

For a local PNG and a deterministic report, the main-body data URI is usually the least surprising option. Use a browser-readable URL only when you intentionally want Chromium to fetch the resource and can control that dependency.

Troubleshooting missing or broken images

The PDF shows a broken image icon or nothing at all

• Verify that fs.readFile() read the intended file and that the process has permission to read it.
• Log the rendered HTML and check the exact data:image/png;base64, prefix.
• Confirm that the bytes are really PNG data and that the Base64 string was not truncated.
• Render the image in ordinary page content before testing a header or footer. This separates data and input problems from special template rendering behavior.

The image is clipped or pushes content onto unexpected pages

• Keep max-width: 100% and height: auto on the image.
• Check the printable width after margins and the selected paper format.
• Set explicit dimensions when a report must have stable pagination.

Colors or backgrounds differ from the browser preview

• Remember that page.pdf() uses print media unless you call page.emulateMediaType('screen').
• Set printBackground: true when backgrounds are part of the design.
• Review print-specific CSS and, where needed, -webkit-print-color-adjust.

The page is captured before a processed image is ready

page.setContent(html, { waitUntil: 'load' }) waits for the document load event, but application code may continue processing afterward. Wait for document.images to complete, a known selector, or an application-specific readiness signal before calling page.pdf(). The example above resolves image load and error events explicitly.

A header logo fails after a Puppeteer upgrade

Check the installed Puppeteer and Chromium versions first. The historical 2018 maintainer comment and the 2025 issue report describe different environments; neither is a universal compatibility guarantee. Move the image into the main page body when a repeating header is not essential.

The process runs out of memory

Large PNGs become larger strings and are represented in several places: the original Buffer, the Base64 string, the Handlebars output, and Chromium’s page data. Resize or compress source images, avoid embedding the same huge image repeatedly, process jobs with bounded concurrency, and close every browser in a finally block.

Security and deployment checklist

• Resolve and validate server-side paths; do not let an untrusted caller select arbitrary filesystem files.
• Validate file signatures and enforce upload-size and pixel-count limits appropriate to your service.
• Keep ordinary Handlebars escaping enabled. Use triple-stash only for a value validated for the exact HTML attribute context.
• Pin Puppeteer and its Chromium revision in deployment so PDF output changes are deliberate.
• Always close pages and browsers, including on exceptions.
• Log the input path, detected type, byte length, Puppeteer version, and PDF options needed to reproduce a rendering failure, without logging sensitive image contents.

Or skip the browser setup

If what you actually need is a screenshot of a public webpage rather than a PDF containing your own local PNG, ScreenshotNeo provides a single HTTP request instead of a Puppeteer installation. Its API accepts cleanup options that remove cookie-consent banners, newsletter popups, and chat widgets before capture; each step can be turned off. Only clean shots are billed: bot checks or CAPTCHAs, blank pages, timeouts, failed loads, and cache hits cost nothing, and the response identifies the result with X-Page-Verdict and X-Billed headers.

For the API parameters and all capture options, see the ScreenshotNeo documentation. A one-call example is:

curl -G "https://api.screenshotneo.com/v1/shot" -d access_key=YOUR_API_KEY --data-urlencode url=https://stripe.com -o shot.webp

ScreenshotNeo also offers an MCP server with take_screenshot, get_page_info, and capture_pdf tools for Claude, Cursor, and other MCP clients. Every plan includes the full feature set, including full-page capture with lazy images loaded, CSS-selector element capture, dark mode, device presets and custom viewports, retina scale, PDF controls, custom CSS and JavaScript, clicks, waits, request blocking, headers, cookies, user agents, authorization, timezone and geolocation, transparent backgrounds, resizing, chosen-TTL caching, signed links, asynchronous webhooks, bulk capture of up to 100 URLs per call, a usage API, and an OpenAPI specification.

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FAQ

Does converting the PNG to Base64 modify the original file?

No. The example reads the file into memory and encodes those bytes for transport inside HTML. The source file remains unchanged.

Can the same generated HTML be used for a browser preview and a PDF?

Yes. Handlebars produces ordinary HTML; you can send that string to a browser preview or to Puppeteer. The PDF-specific differences come from print media, page size, margins, and PDF options.

Is a data URI required for every image in a report?

No. It is the most direct way to carry a server-local file into browser-rendered markup. A browser-readable URL is another option when you deliberately provide a reachable resource and accept its loading dependencies.

Frequently Asked Questions

Does converting the PNG to Base64 modify the original file?

No. The file is read and encoded in memory; its contents on disk are unchanged.

Can the same Handlebars output be used for a browser preview and a PDF?

Yes. It is ordinary HTML. PDF-specific differences come from print media, page dimensions, margins, and PDF options.

Is a data URI required for every image in a report?

No. It is the simplest way to carry a server-local file into Chromium; a reliably reachable browser URL is another valid strategy.

The Bottom Line

Read the PNG in Node.js, embed its Base64 bytes in a correctly typed data URI, render that URI with Handlebars, wait for the image, and then call Puppeteer’s page.pdf(). Keep the image in main page content for the most predictable result, and verify the installed version before relying on data-URI images in PDF headers or footers.

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