Thank you Chouby, my php knowledge is growing by the day but is not yet so good I can follow up on your answer. But I'm happy because now I know there is a way to do this.
I believe, with more and more high res screens, more developers will have a need for this.
So I'll study and see if I can code this.
Meanwhile, if there's anybody out there who already did, I'd be grateful if he posted it. :-)