have tried a number of skins from different authors. also added and deleted images. there doesn't appear to be any issue with jpg files in other programs.- including inserting images into documents, etc.
when published - the same thing - no jpgs - the pages appear fine and all png files appear...
Well, we can't just guess, having never seen this symptom before. We're going to need, at a minimum, a link to an album that shows this problem. And make sure you have enabled the creation of the lifeboat file - we don't want to play 20 Questions.
Yes, this does look like an integrated browser problem, but I can't reproduce it. The project settings are all perfectly normal, and I ran the site through a code validator, and everything is fine.
If switching to an external browser for previews fixes the problem, I'd suggest doing a clean reinstall of jAlbum. It will take only a few minutes, and might clear out some old JAR files that are causing mischief.