Joomgallery Cannot Find Original Images

I am using Joomla 3.10.0, PHP 7.3.32 and Joomgallery 3.5.1.

Jommgallery cannot find its original images in the "Original" folder. Thumbnails are found in their respective folder and all have the same file names as their related original file. When I select an image to see the original, the image border is displayed for a brief moment before disappearing. The log file shows no errors.

Help urgently needed, so I shall appreciate comments.

Having investigated further, I find that all the image files are listed as orphans. However, the thumbnails are displayed correctly but the original images are not found.

How can an orphaned thumbnail file be displayed normally?

Thanks very much for the reply - it is appreciated. Since posting, I have discovered that the cause of the whole problem is a hack - and a brutal one at that! I have had to revert to an older backup and all is now OK except that I have to repeat quite a bit of work.

Thanks again for the feedback. No, I havn't been able to identify the cause beyond the fact that something was injected directly into the database. No alien files seem to have been added. So it is worrying. I will just have to keep very much up-to-date with backups.