Whether I upload via FTP or the web-based upload in admin, if I upload PNG or GIF, I get a blank image in the gallery, but JPGs work fine. The file sizes are all around 100-150kb. Changing the theme doesn't matter. Version 1.2.9

http://romangraphics.net/gallery/

Any ideas?

You probably need to check if your server's GD libary maybe has no support form PNG and GIF. Best you contact your host.

Also review the troubleshooting, the filesize does not matter, the dimensions do.

I am checking with the host, but I know for sure they do support PNG & GIF, since I have 6 other ZenPhoto sites running on their servers with no problem.

One of the images I was working with is 254x600px. JPG is fine, PNG & GIF is not.

Well, then I don't have any idea as all formats do work for me both locally and on my live server. You could open a ticket and attach or if they are too big link to them so we could take a look. My guess would be that they are somehow corrupt.