Super Screenshot is a free web service that let you capture any page and save the output as a JPG or PNG image file. To make a screenshot, you enter a website URL, screenshot that download the URL in a browser, renders the HTML, and the page is captured to a file. If the web page contains a lot of images or advertisements, it can take several seconds to load the page.
You get a few options with Super Screenshot, like the ability to capture a whole page or just the top of the screen. You can also select the size of the final picture, but you don't get to set pixel heights and widths. Instead you get some rather unhelpful options like X-Small, Small, Medium, Large, and Full. So you might need a little trial and error time to find the right size.
Relative read: WebShotsPro: AJAX Driven Website Screenshot Creator
Website, Screenshot, Web Service