Starting a comedy website, and I have a question about using images found on the internet.

Many images on the internet are copyrighted, and their rightsholders have the exclusive rights to exhibit them, reproduce them, distribute them, etc. But yes, "fair use" allows exceptions, and there's a 4 part test involved, weighing the purpose and character of the use, such as whether your use is commercial, non-profit, educational), the nature of the copyrighted work, the amount of work used in relation to the copyrighted work as a whole, and the effect of the use on the copyright work's potential market.

You may be able to find free non-copyrighted public domain images for your "dumpster"-type image needs, or get very cheap licenses from reputable stock photpgraphy houses, or just take your own photos and use those. The fact that your site will have paid ads isn't conclusive as to it's commercial nature, but it's indicative of it, and your use is pretty clearly commercial, so all of that leans against you in the fair use calculation.

As for photos of celebrities, besides the rights of the photographers who may own the photos if they didn't sell them to the celebrities, the celebrities have "publicity rights" to exclusively exploit their own images for profit. But those rights are limited, too, by everyone's 1st Amendment rights to mock and parody these famous people, like The Simpsons does, and like South Park does. It's trickier with trademarks like Superman's "S," because a kind of tradmark infringement is when you "dilute" or "disparage" the trademark by using it in a negative way.

In general comedins have a good shot at getting a free pass in using and mocking other people's protected work, since commentary, especially of the political and social type, is given pretty broad protection. But you still have to be careful you're not negatively affecting the market for the protected works, and unfairly competing, and using celebrities images just to trade on their fame without a legitimate (mis)use of their images. No one can advise you in the adstract of whether your concept for this site will get you sued for infringement or not, so you're best off running some samples of your site past an IP lawyer who's experienced with the issues that tend to get people sued.

Disclaimer: Please note that this answer does not constitute legal advice, and should not be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue. This answer does not create an attorney-client relationship.

You will not find better advice than Ms. Koslyn's. Hire her or someone else familiar with intellectual property to walk you through this minefield.