Iain, PHP can help... sort of. I think you're describing a client-side app that is usually developed in VB, VC++ or similar language. PHP is designed primarily as a web server add-in to allow quick development of dynamic web sites.
The first part of what you describe (grabbing images and saving them to disk) can be accomplished with the functions fopen/fread/fclose.
But the printing part I'm not sure how you would accomplish (I'm assuming a Win32 platform). If this truly is a client-side app and not a web app, I would recommend using something like VB for rapid development (it's pretty straightforward, too).
Dave
===========================================
http://badblue.com
Free small footprint web server for Windows
P2P file-sharing, PHP, wireless apps & more