Karen
The Karen tribe is the largest of the hill tribes in Thailand, while world-wide they consist of over 7 million people (about the same population as Hong Kong and Switzerland). They have their own flag, and is the only tribe in Thailand with their own written language. If you would like to see what their written language looks like, check out this Karen news website for an example. To the untrained eye, it looks very similar to Burmese and Mon . . . which makes sense, considering their related history.

The famous ‘giraffe’ women are a small subset of the Karen tribe. The heavy rings around their neck push the shoulder bones down, making the neck appear long (but it is not actually stretched). They believe a long neck is a sign of beauty, but also is considered a must-do tradition. Their villages are often described as ‘human zoos’ due to the strong negative influence of tourism on their lives. Tourist operators and government officials often ban the women from leaving the villages.

As there are no real stereotypical Karen outfits, there is no easy way to identify the typical Karen. So I have no pictures for you.

Hmong
The Hmong is the second largest hill tribe group in Thailand. Most of the Hmong in Thailand are refugees from communist Laos during the cold war. Some have been forced into refugee camps and later force-repatriated by the Thai government ( source).

Although most Hmong gave up their traditional outfits by the 90’s, there are several stereotypical outfits that the women occasionally wear that can help you identify them. The most common one you’ll find in Thailand is as shown in this image:

image: Hmong women wearing traditional outfits made from modern materials

Occasionally you’ll see very young children at popular tourist destinations wearing these outfits, singing and dancing all day every day. They’ll take pictures with you in exchange for 10 baht and some candy, and seem to enjoy their ‘job’. Their mothers aren’t far away, watching for their safety.

Google offers many more pictures of traditional Hmong outfits. And this site has more Hmong pics.

This is one of my favorite Hmong songs. As you can see they’ve modernized quite a bit!
http://www.youtube.com/watch?v=4PhOh5P17y0