However, there are third-party apps available to ease the task of capturing custom sized screenshot. Here are my two favorite programs.
Mac App 1: All you have to do is to enter the website URL, set a custom size and the screenshot is generated. This is exactly how Paparazzi works.
Paparazzi is a free screen capturing utility for Mac OS that lets you input the URL of a webpage, crop the captured screen and batch capture webpages with a custom size preset.
Plus, if you don’t want to crop pictures every time you capture a screen, setting a custom size is definitely going to save you some time. There’s nothing too fancy about this app. It does exactly what you want: generate a screenshot of a particular webpage.
For the price you pay, which is free, this is a handy little gem for every Mac user.
Download Paparazzi (Works on Mac OS X Lion and Leopard).
App 2: Capturing image from the web world is really easy with Instant Shot as the program comes with options to capture, convert images & save them to JPEG, PNG or in TIFF format.
You can capture full screen or a part of it and add fixed borders or resize the captured images. All in all this freeware utility does exactly what you need – capture screens with simplicity!
Download Instant Shot [For Mac]