security - Secure dynamic images. PHP -

i made php script create 1 of several dynamic images used backgrounds elements on webpage. question not coding question , code works great, far.

my question implementation , possible security issues using pass data bg.php . right scr of image looks

../bg.php?t=1&w=200&h=200

where
$t type of shape. (array of polygon coordinates)
$w width of image
$h height of image

is using safe functionality, or there better/safer way of passing variables bg.php?

bg.php called several times per page , used in <img src="bg.php"> <style>bg.php</style> , <script>bg.php</script>

someone malicious render image of size, assuming don't check this, use memory/storage on server.

hj