I have one that I use on many sites, and am now adding both the MySQL (for text for images, and image control) as well as the imagemagick for resizing. I have a great deal finished, and the entire project was actually a lot more simple than it might seem. Give it a shot, you will probably find it easy as well.
I hope you found this answer when your manager told you to "just Google it".
Ubuntu 10.04 LTS | Vim | Chromium/Google Chrome
Intel Core 2 Duo | 8 GB DDR2 | 2x 500 GB WD HDD | ATI Quad Head | 3 22" AOC Monitors
And of course there are hundreds gallery scripts already out there, one of which likely meets your needs. So depending on your requirements, schedule, and budget; you may need to consider whether the learning experience is worth the time it will take to "roll your own" as opposed to using something already out there.
To be honest, a lot of the stuff I ask about I'll probably never use for my own personal site. I'm interested in becoming a professional web developer/programmer, though. I like to be able to code my own applications as much as I possibly can.
I probably will, at some point. At this point, I don't know if my website will ever need an image gallery (depends on how much it grows and what the members want), so it would be kind of a shame to build one and never have any use for it. But then again, if I don't attempt it, it's always going to nag at me in my head (just the way I am).