I GOT IT TO WORK!!!!!!!!!!
For awhile I couldn't stop laughing. The only thing wrong was this little bit of code right here:
if (!extension_loaded("GD")) <-- occurs twice
"GD" needs to be "gd" lowercase. Can't be uppercase. This is incredibly funny because it's so ironic that it was that simple. My guess is that, at the last minute, Josh decided to add that bit in, realizing that some people don't have GD extensions. Since we normally capitalize abbreviations, it's natural to write the code that way, but some servers apparently only recognize "gd" in lowercase.
For somebody installing this for the first time, it's simple to just go through the modification instructions and make those 4 replacements. If you've already installed it, then it's easier to open up the files and make the changes. They are
includes/usercp_register.php <-- "GD" occurs twice
And don't forget to put *unique* photos in your library and maybe customize the question to the theme of your forum. I'm going to bed, but I'll probably say something like "Put a checkmark next to mountain climbing photos. Do not click on household appliances." The nice thing about that one is that the mountain photos will have a lot of snow, and some household appliances are white, so that would mess with any spambot trying to crack my photo library.