Stumbled on this by accident.... If you include a GIF in your project (animated or not - doesn't matter), jAlbum converts it to a PNG. Photoblogger is unable to display the slide image. It has no problem with images that start out as PNG's.
It gets even weirder. If you take the output PNG from a project, one that's been converted by jAlbum from a GIF, and use it in a new project, Photoblogger has no trouble with it.
Story suffers from the same difficulty, but not the other "Laza" skins.
A demo: (demo album removed)
Original GIF's attached - one animated, the other not.
This is happening on Windows and macOS, so it's clearly not a problem with something like file permissions. But I agree, there's no GIF file in the output.
I'm not clear about what your skin is doing. In my skins, I simply detect a GIF in the image directory, and just do a quick obj.setUseOriginal(true). The skin itself doesn't do any file copying to the output - at that point the jAlbum core takes care of it. It copies the GIF to the root of the output, and doesn't bother generating a PNG.
The code says the file has been successfully copied. In the case of using "album", jAlbum removes the file, and when I use an external folder it doesn't. I tried another copy method - Files.copy() - which does the same. I believe jAlbum should work the same for both folders.
When my skins were still doing the file copying, I believe I did it in postdir.bsh, rather than predir.bsh. Now I do a simple recursion in init.bsh, where I set the GIF's to Use original (I also exclude unsupported objects while I'm at it). Much cleaner.