Signature cut-off
 

Can someone tell me how to cut signatures off at a certain height or width. I've edited it so people can't upload a signature pic past 180 pixels tall, and I've limited the amount of characters and lines in a signature field, but people on my site are able to link signatures that are like 600 pixels tall and it's become annoying. Is there ANY way at all to limit signature size, besides character count? Because all people need is 30 characters and one line to make a gigantic signature.