Hardware Secrets has posted an article on Digital Cameras

Megapixel is a unit that measures the resolution in optical devices (i.e., the number of dots the image will have), especially in digital cameras. The value in megapixels is found by multiplying the image’s width by its height. For example, an image with resolution of 1280x1024 has resolution of 1,310,720 pixels or 1.3 megapixel. On the chart below we present the most common resolutions. As you can see, there are some close estimates: cameras with 1.9 megapixel are sold as having 2 megapixels.

Everything You Need to Know About Digital Cameras