A lot of the professionals use a program called Adobe Photoshop. They can do incredible things with it, including anything from resizing a picture to making incredible pieces of video art. It can be a fairly expensive program though. Last I checked, it was close to $200.

There is another program that has been out for many years that is kind of a "lite" version of Photoshop. It does many of the same things, but just doesn't have all the bells and whistles. It is called "Gimp." It can be downloaded for free here. With a little practice, you could be putting out some awesome memes with Gimp! :)