I started showing my girlfriend's pictures to strangers I came across on a dating app.
What was the reason why you were showing these pictures to strangers?
This is the only way I can hurt her as much as I want.
You cannot use someone else's pictures without their consent. This is harmful and illegal behavior.
I just did it as a big joke so she would find out and laugh.
Well hopefully these were not pictures that showed any part of your girlfriend that were explicit. This would be a huge invasion of privacy. Be careful with the way you decide to make jokes when it involves other people!