The Frinkiac is a search engine and web site that shows screen caps from The Simpsons related to a phrase or word entered. It claims to have over 3 million screen caps.
It's not clear if this site has the legal rights to show these screen caps, but Matt Groening has a history of being lenient on derivative works. FOX and other related copyright owners may not be so lenient.
An example of Frinkiac's image-captioning feature, based on a screenshot from the episode "Homer Badman". The original image can be found here.
Another example showing how the captioning feature can be used to incorporate memes, based on a screenshot from the episode "Marge Gets a Job". The original line was, "Let me be the first to say, kabebu kazini." The original image can be found here.
The logo's image was taken from the episode Bye Bye Nerdie, where Frink shouts that "Pi is exactly three" in order to make a group of nerds quiet. However, in contrast to the cel animated original scene, the website's logo is colored digitally.