The internet is a very dynamic place. Sites, images, and resources are always coming and going. Controversial content is purposely removed by originators or site hosts. Site redesigns more often than not break links to images or navigational elements.
A good place to start:
The Internet Archive has a tool called the Wayback Machine that takes snapshots of webpages as they appear when the page was saved. By now many people are aware of it’s existence, but I would bet that few people know you can manually innate a capture with their “Save Page Now” feature. Only caveat is that it is “only available for sites that allow crawlers.”
Wayback Machine – See how a page appeared when a snapshot was taken.
Wayback Machine “Save Page Now” – Capture a web page as it appears now for use as a trusted citation in the future.
DownThemAll! – add-on for Mozilla Firefox that “lets you download all the links or images contained in a webpage and much more”
web-capture.net – an online tool that saves an entire webpage (better than stitching together multiple screenshots). Save in JPEG, PDF, TIFF, BMP, PNG, PS, or SVG formats.