Understand how source files are replaced
Image Optimizer replaces the attachment’s main file after successful processing, keeping the same filename and URL. It does not maintain a permanent “originals” archive that an administrator can restore later.
Protection during processing
The module processes a separate temporary copy and checks that the finished image can be fully decoded before replacing the source. A readable header or a non-zero file size alone is not sufficient. If compression, validation, or replacement fails, the source file remains unchanged.
Each source image and WebP companion is replaced atomically: visitors receive a complete file while processing runs. If the filesystem cannot perform the replacement, the module reports a failure and keeps the previous file. Temporary working files are removed when the attempt ends; they are not a recovery archive.
If the source succeeds but a later WebP conversion fails, the validated source remains optimized and its dimensions and file size stay accurate. An existing companion is kept until a valid replacement is ready. The attachment remains eligible for Optimize missing images so companion generation can be retried.
What a successful run changes
A successful run can:
- resize the main image when its longest side exceeds 2560 pixels;
- compress and overwrite the main file;
- update stored width, height, file size, and savings information;
- create WebP companions for the main file and generated sizes;
- remove generated variants for that attachment that no longer belong to current metadata.
Optimize all images also clears the module’s completed marker before rebuilding the selected attachment metadata.
Prepare a recoverable test
- Copy the uploads directory and database to a restorable backup.
- Select images that represent transparency, large dimensions, photography, graphics, AVIF, GIF, and existing WebP.
- Record each original filename, dimensions, file size, and attachment URL.
- Optimize only the test set first.
- Compare visual quality at full size and every frontend crop.
- Keep the external backup until the production review is complete.
Recover an earlier original
Disabling the module cannot reverse a successful overwrite. Restore the required file from the pre-operation backup, then regenerate attachment sizes with an approved WordPress media workflow if necessary. Verify that attachment metadata and frontend URLs still describe the restored files.