With most sites, their terms of service covers them and make it the responsibility of the poster to have the rights to use an image. Still, that doesn't stop someone from suing them.

User contributed content (that is, content uploaded by external users, not the site owner or staff) gets a little bit of a "get out of jail" free card. Under the DMCA, the site owner will be contacted and requested to remove the copyrighted material, but typically without penalty (unless there is gross violation, such as encouraging uploading copyrighted content).

As a blog owner, you have more risk. Since it's not user provided content, you are responsible for verifying the license and accountable for damages if any infringement occurs.

Thanks for your great answers!

I heard that some people got sued but they were not in the same country so they just ignored it and everyone moved on.

Weird but that is what I heard.

some times they just don't pay attention, some other times people do not get in trouble of suing , some other times under their T&C they make it responsibility of the uploader and so on ... so many ways to just get rid off the responsibility

A lot of memes and images on sites like 9gag could be protected from violating copyright under 'fair use' such as parody or satire.

The site itself is somewhat protected by laws governing 'user generated' content.

A friend of mine nearly got sued for using copyrighted images, he had no idea because the web designer used the images when making the site... nearly a few years later he was contacted by getty images. They were willing to settle for a specific amount of money per image but it was quite large. My friend got a lawyer and wasnt giving in, in the end he ended up using up a lot of money in lawyers fees but didnt have to pay getty.

If you google Getty you will see tons of information regarding lawsuits.

For one thing, never ever get your images directly from Google. Look for images on stock image sites. You can get a lot of stock images for cheap, and even free images to use although those are usually not as good. If you're a war room member, you can actually find some really good quality stock images to use shared by members in there

Well, you'll only be sued for sure if you use copyright content without acknowledging the owner. Or if you want, try getting a website host off-shore. That way you won't be sued easily.

For some like getty images acknowledging isn't enough..