When you find a picture that you like you right click on it go to properties at the bottom then when it pops up copy the URL that is there. Then you come back and hit the IMG button above ( I FIND IT EASIER TO DELTE THE HTTP THAT IS ALL READY THERE) and paste it right there.
If you need more help let me know.....I had to ask for help with this also and a fellow board member got me right through it.