If Finder is showing generic image icons instead of pictures, open the affected folder in Icon view, choose View > Show View Options, and enable Show icon preview when that option is available. Then test the same file with Finder’s Preview pane and Quick Look. Those checks tell you whether Finder’s icon setting is the problem or whether the image itself is not previewing.
Start with the folder’s Finder view
- Open the folder containing the images.
- Choose View > as Icons (or click the Icon view button in the Finder toolbar). Icon view is the Finder presentation intended to show files as large thumbnails.
- Choose View > Show View Options.
- Turn on Show icon preview if the checkbox appears. Finder view options can be stored per folder, so changing the setting in one directory may not change another.
Return to the folder and give Finder a moment to redraw the icons. If thumbnails appear, the problem was the folder’s presentation or icon-preview setting. If the checkbox is missing, use the other preview surfaces below to determine whether the failure is limited to icons.
Check whether the image can be previewed at all
Use the Preview pane
Select an image and choose View > Show Preview. Finder opens a preview pane for the selected item. View > Show Preview Options exposes controls that vary by file type, so you may not see identical options for every image.
Use Quick Look
Select the file and press Space. Quick Look should open a larger preview without launching a full image editor.
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If the Preview pane or Quick Look displays the picture while the file icon remains generic, the image is readable and the symptom is specifically Finder’s small icon preview. Continue with the icon-setting and thumbnail-agent steps. If neither surface can display it, investigate the file, its format, or the folder more broadly rather than treating this as an icon-only problem.
Use this symptom matrix to choose the next step
| What you observe | What it tells you | Next action |
|---|---|---|
| Only one folder lacks thumbnails | A per-folder Finder view option is a likely place to start. | Switch that folder to Icon view and enable Show icon preview. |
| Many folders lack icon thumbnails, but Quick Look works | The images are previewable; the failure is concentrated in Finder’s icon-preview path. | Recheck Icon view, then try the optional Quick Look thumbnail-agent restart. |
| Preview pane works, Quick Look works, icons do not | The file itself is not obviously unreadable. | Focus on Show icon preview and Finder/Quick Look processes. |
| Preview pane and Quick Look both fail | This is not proven to be an icon-only issue. | Record the image format, macOS version, and affected locations before seeking support. |
| Some formats preview and others do not | The available preview behavior can differ by file type; no complete format matrix is established here. | Note the exact extensions and test a known-working image in the same folder. |
Restart the thumbnail process (optional workaround)
Mac users have reported that restarting com.apple.quicklook.ThumbnailsAgent and then relaunching Finder restores missing icon previews. This is a community-reported, version-dependent workaround—not an Apple guarantee that it fixes every thumbnail failure.
- Open Applications > Utilities > Activity Monitor.
- Use the search field to find
com.apple.quicklook.ThumbnailsAgent. - Select that process and click the stop (×) button.
- Choose Force Quit when Activity Monitor asks for confirmation.
- Open the Apple menu, choose Force Quit, select Finder, and click Relaunch.
- Return to the image folder, select Icon view, and check whether thumbnails are rebuilt.
Because reports of success can be temporary and depend on the macOS release, do not treat this process restart as a universal repair. If it changes nothing, continue documenting the scope of the problem instead of repeatedly killing the process.
Confirm that the file, not just its icon, is the problem
- Test one image that normally previews and one image that does not in the same folder.
- Compare the file extensions and note whether the failure follows a particular format.
- Move a copy of an affected image to another folder and test it there. A result that changes with the folder points you back to per-folder view settings; a result that follows the file suggests an image-specific issue.
- Use both the Preview pane and Quick Look. Their results are useful diagnostic clues, but they do not by themselves identify a single root cause.
The available guidance does not establish a universal cache-reset command or a single cause shared by every macOS version. Avoid deleting unrelated Finder data or running undocumented cleanup commands when the evidence only supports checking view settings and, optionally, restarting the thumbnail agent.
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Troubleshooting branches
“Show icon preview” is enabled, but icons are still generic
- Verify that the window is actually in Icon view; List, Column, and Gallery views present files differently.
- Close and reopen the affected folder after changing the option.
- Test Preview pane and Quick Look. If they work, try the reported thumbnail-agent restart once.
- Check whether the issue affects one folder or many and record that result.
Quick Look opens, but the image is blank
Try another image in the same folder and record the format and macOS version. A blank or failed Quick Look result means the issue is not demonstrated to be only a Finder icon problem, so seek current Apple support with those details.
The Preview pane is not visible
Select the file, then choose View > Show Preview. The pane is separate from icon previews; turning it on does not automatically enable thumbnails on file icons.
The problem returns after a restart
Recheck the affected folder’s view options and note whether the failure is limited to particular directories or formats. If the workaround only helps temporarily, include that fact when contacting Apple support; it is useful diagnostic information, not proof of a specific underlying cause.
Only one image never previews
Compare it with a known-good image and test it with both Preview pane and Quick Look. Preserve the original extension and note any difference before converting or editing the file, because changing it can obscure the original symptom.
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What to record before asking for help
Support can investigate faster if you provide a compact reproduction record:
- The exact macOS version.
- The image extensions that fail and one extension that works, if applicable.
- Whether the issue appears in one folder, several folders, or nearly everywhere.
- Whether Icon view and Show icon preview were enabled.
- Whether the Preview pane and Quick Look display the same files.
- Whether restarting
com.apple.quicklook.ThumbnailsAgentand relaunching Finder changed the result, and for how long.
This information distinguishes a folder-view symptom from a broader preview failure without assuming a cause that has not been confirmed for your macOS release.
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Frequently asked questions
Frequently Asked Questions
Does Finder have a guaranteed thumbnail list for every image format?
No complete, current format-compatibility matrix is established here. Record the extensions that work and fail, then provide that information to Apple Support.
Will changing the Preview pane setting turn on icon thumbnails?
No. The Preview pane and icon previews are separate Finder features. Use Show View Options and enable Show icon preview for file icons.
Is restarting com.apple.quicklook.ThumbnailsAgent an official Apple fix?
No. It is a community-reported, version-dependent workaround. Apple’s documented controls cover Finder views, the Preview pane, and Quick Look, not a guarantee that restarting this process resolves every failure.
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What should I do if thumbnails fail everywhere after these steps?
Document your macOS version, affected formats, folder scope, Preview-pane and Quick Look results, and whether the process restart helped, then seek current Apple support.
The Bottom Line
Use Icon view and enable Show icon preview first. Test Preview pane and Quick Look to separate an icon-only symptom from a broader image-preview failure; only then consider the reported thumbnail-agent restart and gather version, format, and scope details for support.
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