Passing variables to PHP with IMG Tag

[jvalarta]

I am passing variables from a customer's website that doesnt support PHP, to a server that does, like this:

<IMG SRC="http://www.domain.com/index.php?var=this">

This works perfectly, but the PHP script takes a few seconds to run (as it's doing a bunch of DB stuff) and I need to speed this up. (I believe Ive got the db stuff fully optimized, there is no option for speed increase there)

My question is, is there a better way to do this, or is there some way that the PHP can deliver an image name and keep running to process, without holding up the loading of the page (waiting on the image)?