For images that I've uploaded via FTP, I can't delete them from the admin front end. However, when I tried uploading an image from the GUI, I could delete it from there too. Is the problem with the deletion a possible bug?

Can you provide some more information? Filenames of the image you can delete and of the ones you cannot delete. Can you delete them via FTP? It is possible to upload files with PHP which have characters in them that prevent zenphoto from dealing with them.

I am having a similar problem. I'm using Stoppeddesign and when I try to delete a photo from an existing album I get the following error message:
Warning: unlink(/home/mileseng/public_html/zenphoto/albums/imoc_07/P1020058.jpg): Permission denied in /home/mileseng/public_html/zenphoto/zen/class-image.php on line 99

Warning: Cannot modify header information - headers already sent by (output started at /home/mileseng/public_html/zenphoto/zen/class-image.php:99) in /home/mileseng/public_html/zenphoto/zen/admin.php on line 86

Any thoughts?

If you mean deleting images that you uploaded from the file system, it might simply be a matter of permissions. When you upload via FTP, you own the files, not PHP. And the default permissions are probably something like 644. Try chmod 777 on your uploaded files.

Good call, for some reason just the album/folder I was working in had it's permissions set to 755 instead of 777. I changed it and it's now good. Thanks for the quick reply!

I may have spoke too soon! Now I can't change my theme back to Stoppeddesign. I changed to default-dark while I was trouble shooting. I wonder if I inadvertently changed a permission that is now not allowing me to change themes. What controls the ability to swap themes? I did check my themes folder and all the themes are there. And it's not just Stoppeddesign I can't use - I can't change from default-dark to anything.

Forget it, I searched the forums and found a suggestion to delete the theme.txt file from the cache folder. That worked and I'm back to my preferred theme.