Here are some pictures of head lice, nymphs and eggs (also called nits) using various magnification levels.
Here is a picture of an adult louse and a louse nymph (immature louse) on a dime. The adult is about the size of FDR's ear, and the nymph can fit easily inside his ear. Although it is magnified a bit, it gives you a better sense of how big lice are compared to some of our other photos.
This picture shows a number of dead lice on multiple strands of hair. It uses roughly the same magnification as the dime picture.
This micrograph (taken by Tabitha L. Allen of Rapunzel's Lice Boutique) compares the size of a first-stage nymph with George Washington's eye on a $1 bill.
Here is a picture of a head louse moving along two strands of hair. Notice how it wraps its claws around the hair shaft. Because lice don't jump, they use their claws to move from the hair of one person to another during head-to-head contact, which is the primary way you can get lice.
Here is a picture of four head lice, ranging from three sizes of nymphs to an adult.
This micrograph (taken by Tabitha L. Allen) shows a nymph that apparently died while emerging from the casing of its egg.