You might want to further go through and patch any security holes in scripts that you hand-wrote. Make sure nothing allows a user to inject headers (for example, in a email sender) or upload files with filetypes other than specific ones (ie: allow jpg, prevent .php or .asp or whatever).
If you are running on Apache (your gallery uses php files, so I will assume this is true), you can also use .htaccess files to block IP addresses of known offenders. A nice look at .htaccess can be found
here -- they're quite useful for many things.
Also, I don't know if anyone told you otherwise, but your site is built using tables. There's nothing wrong with that, but if you are hoping to grow as a web developer, look into learning CSS and using it for layout as well as style. Alistapart.com (A List Apart) is a pretty amazing site for web design concepts in general. The table vs. CSS debate can be found
here.