I just had a lot of trouble changing my avatar. All those "I am not a robot" challenges. arrgh! But I succeeded---after about 15 minutes of it.
The key to it is making it a game. Those imbecile Deutsche Bahn railway ticket machines over here have a lot of trouble recognizing euro bills so I usually enter the train station 20 minutes early and count the rejections of the same bill out loud.
If I get impatient and try another ticket machine, I lose the game, and if I try another bill, I also lose. You also have to look cool, so if I start cursing or kicking the machine, I lose. I mostly win eventually.
My record is 32 rejections.
Also, when these things crap out the change to a 16€ ticket / 50€ bill in coins, I always scream "JACKPOT".