An image can fail before reaching the server, while being saved or while WordPress generates resized versions. Check the exact message and whether an attachment exists before retrying the same file.
Compare one small supported image with the failed file, then investigate the stage the evidence identifies.
Guide reviewed: October 8, 2026. Interface labels may vary by version, account and device.
Quick diagnosis
| Evidence | Stage | Next check |
|---|---|---|
| 413 or explicit size rejection | Request transfer limit | File and whole-request allowances. |
| Temporary folder or disk-write message | Server storage | Directory, ownership and capacity. |
| Original opens; previews missing | Image processing | Dimensions, image editor and logs. |
| One file fails; known-good file works | File-specific | Re-export a copy in its real supported format. |
Begin with one image and the full message
Use a small, non-sensitive image in a common supported format as a comparison. Upload it by itself rather than repeating a large batch. If it succeeds, compare its format, dimensions, and file size with the image that failed.
If both fail, note whether the message appears immediately or after progress is shown. Timing is evidence to report, not a diagnosis on its own. The request response and server logs are needed to explain the failure.
WordPress’s official media-upload guide describes the file picker and, where offered, a browser uploader alternative. If drag-and-drop is the only part that fails, try the normal Select Files control. That tests the interface without changing server settings.
Separate file size from image dimensions
Comparison note: record both bytes and pixel dimensions. A highly compressed image can still have many pixels to decode and resize. Use a copy suited to the intended article display and keep the original.
The upload screen may show a maximum file size. Check that value and any explicit size message first. A 413 response, for example, concerns an accepted request-size limit and needs a different investigation from a file-type rejection.
Image dimensions are also useful information for the maintainer. A compressed picture can have a modest file size while still containing many pixels. WordPress uses image-editor implementations such as GD or Imagick for operations including resizing and saving; an upload includes more than transferring bytes.
For an article, export a copy at dimensions suited to its intended display and retain the original for editing. Check the copy visually. The aim is a useful image, not reducing it until labels and details become unreadable.
Check whether the original arrived
Look in the media library for an attachment from the attempt and open its file link if available. A working original with missing previews gives the developer a different lead from an upload that created no usable file.
If the original is present but processing failed, provide the dimensions, format, and failure time. Ask the host or developer to inspect the image-processing result and its logs. Increasing a setting at random may not affect the component that failed.
If the message mentions a missing temporary folder, a disk write, or a failure to move the file, preserve that wording. Those messages concern server storage or access stages and should be investigated accordingly. Renaming the picture does not restore a missing working directory.
Follow a focused troubleshooting path
- Check whether the previous attempt created an attachment.
- Upload one small non-sensitive comparison image.
- Compare format, dimensions, message and timing.
- Ask for logs from the identified transfer, storage or processing stage.
If the problem affects only one file, re-export a copy through a trusted editing application and compare it with a known-good image. Do not merely replace its extension. The exported contents need to match the intended format.
If every file fails after a hosting or PHP change, ask the provider to review that change with the exact failure time. If a particular upload feature fails while the main media screen works, give that comparison to the feature’s maintainer.
For a recent plugin change, use a controlled test environment where practical. Avoid taking multiple live features offline at once. A focused comparison gives you a clearer explanation of what changed and what restored the upload.
Verify the image in normal use
After the correction, upload one suitable test image and check its library preview and original file. Insert it into an article preview and confirm that it displays at the intended size. A completed progress bar is only the first part of the result.
Inspect earlier attempts before cleaning them up. Similar filenames do not prove that an attachment is unused, and deleting a file used by another article can break that article. Keep the cleanup tied to known test files.
Save the confirmed failure stage and correction in a short note. That makes a future upload issue easier to recognize and helps you avoid repeating a long list of unrelated changes every time a picture fails.
References: WordPress’s media-upload guide and its image-editor reference.
Confirm the image in the article
Verify the library preview, original file and article preview at the intended display size. Review earlier attempts before removing known test attachments; a similar filename does not prove a file is unused.