Quick summary

Imagen couldn't read one or more photos while preparing them for upload. The file's content isn't in a format Imagen can read, or the file is damaged.

How to fix this

1. Try to open the photos in another viewer. If a photo won't open or looks broken, it's damaged. Copy it again from the memory card or your backup.
2. Look for photos that were converted or saved by another app. HEIC, PNG, PSD and GIF aren't supported. If the message says a file's extension doesn't match its format, see Error 2195: File extension doesn't match the file format.
3. Remove or replace the photos that fail, and create the project again.
4. Upload the original camera files where you can. Imagen supports RAW, DNG, JPEG and TIFF files.