I don't use photobucket, I use Flickr but I'll try to help.
You are probably referring to a "captcha". It generally wants a user to enter numbers or characters, to prove that you're human and not a "bot" - a computer robot that scours the net for anything and everything.
Make sure you are using the latest version of your browser, for starters. What browser are you using and what device; laptop, iPad, phone, etc?
If you don't like Photobucket you could try Flickr - I've been using it for years and have had no problem with it. flickr.com
Some folks call me Vince - other folks call me...........