Can I use a WP image gallery on a NON-WordPress website?

Most of my websites are NON-wordpress custom sites.

I write most of my own CMS (or as much as I need), BUT I can never seem to create a photo gallery that my clients can update and maintain.

My question is…. Is it possible to create my own website, but use a WP image gallery? If so, how?

I have an i-frame on my photo web page, so I could aim it at a page that has the WP gallery(so I can keep my navigation bars and custom page layout, etc).

Would I have to (or could I) install WP, and just point my i-frame to it?
Just a thought that would solve a lot of my problems.

Any advise or suggestions are very welcome! Thanks.