The only issue is accessing the button's value, which gets passed as an x and y coordinate of where the button was clicked.
Using Dave's example
<input type="image" src="whatever.jpg" name="yourname">
In your script you can't say
if($yourname)
The form will pass to valriables in this case yourname.x and yourname.y which are where the user clicked on the image, so you could use
if($yourname.x > 0)