Here are some pictures of head lice:

Head louse crawling on hair shaft.

Head louse crawling on scalp.

Head louse showing claws.

Different stages of head lice growth.

Different stages of head lice shown in relation to a coin.

Here are some pictures of nits:

A two day old lice egg (nit) attached to a hair.

A nit about to hatch.

An empty egg sac. These white nits are already hatched and are very difficult to remove without some kind of enzyme because they slip right through the lice comb teeth. And with No-Nit Policies in place, they must still be removed, even though they are already hatched and pose no danger in and of themselves.

This nit is dead and will not hatch.

This is not a nit, but sometimes dandruff or other material looks like nits.