There are a couple of web services that offer the exact thing you're looking for. Websnapr is one, Browsershots is (to my knowledge) the oldest competitor in the space.
I tried using Browsershots years ago, and found it really quite slow, so I instead implemented a local version instead. If you're using Linux, you can programmatically launch a browser, take an X-Screenshot, and run that through ImageMagick to crop out browser chrome and OS things.
Offhandedly, I don't know how you'd go about splicing together multiple screenshots to get the long tail of the page, but I'm sure it's doable too, with thought.
That said, websnapr looks faster than I remember browsershots being, and not knowing your requirements, it may be good enough anyway.
I tried using Browsershots years ago, and found it really quite slow, so I instead implemented a local version instead. If you're using Linux, you can programmatically launch a browser, take an X-Screenshot, and run that through ImageMagick to crop out browser chrome and OS things.
Offhandedly, I don't know how you'd go about splicing together multiple screenshots to get the long tail of the page, but I'm sure it's doable too, with thought.
That said, websnapr looks faster than I remember browsershots being, and not knowing your requirements, it may be good enough anyway.