Another, possibly easier, way to do it is to click on the img= button and a little popup window will appear. In the space it provides, put the url you want to link to, then click "confirm" and you will get something that looks like this (img=url link][/img) but with brackets instead of parenthesis. Then you put the pet's image url before the /img as usual, and there you go!

cool^^

(Just Testing)