I can't help you with making it, but to put it on is quite simple.
First, if it's your own image, you have to put it on a image hosting website- I use Photobucket.
Then, this works if you're getting it from the web, you get the image's web address and put it in an image code, by clicking on the Mona Lisa button. Also, on Photobucket, if you right click on the picture, it gives you the forum code already to copy and paste in.
Then you copy the web address in between what you get.