PHP programming forum. Ask questions or help people concerning PHP code. Don't understand a function? Need help implementing a class? Don't understand a class? Here is where to ask. Remember to do your homework!
I don't have a complete answer, but here's some places to look.
First use google to search for "screen scraping", typically speaking the search hits will describe text only captures, not graphics/screen shots, but somewhere there might be a good link or two. Also search for "window capture".
Second. I can think of a possible automated approach being something like
1) use system/exec calls to launch a browser passing in the target site
2) use system/exec to launch the window capture program, pasing in a reference to the newly spawned broswer, with the output of the capture saved to a specified file
There's lots of holes to fill-in, but this should get you started....