I've been trying to find an image gallery that plays nice with our custom CMS. I've evaluated a number of them, but none of them seems to have the feature list that I would like:

• Run on LAMP environment
• Free software or low license costs (the website belongs to a non-profit organisation)
• Multi-user support
• Multiple albums. We're posting concert pictures, and would like an album per event.
• Pluggable authentication system. I want to reuse the accounts we have for our CMS. Permissions can be done inside the gallery itself, but I want to have a single sign on solution in a maintainable manner, by writing my own plugin/add-on for the software.
• Upload support (multiple images at the same time)

And preferrably also:

• Can be integrated into a PHP page layout without IFRAMEs
• Automatic resizing of uploaded images to a maximum size
• Ability for visitors to place comments

This combination is proving hard to find, especially the authentication requirement. I don't want to mess around all over the place in the source code to make it use the existing authentication. A plugin would be ideal, but alternatively a well thought out software design that allows for maintainable surgical changes would be acceptable.

Any suggestions on which software I should take a closer look into?