How do you get pictures on animal crossing wild world?

When the character is angry and has an exclamation mark over their head you go and talk to them for a little bit and be extra nice (e.g. don't push them or hit them with a bug net). Once you have talked to them about 3 times go away for a minute to let the character calm down and go and talk to them and they may say you can have my picture. If this doesn't work then sometimes when you have had a chat to a few of the characters and you walk straight in front of them the will have a little exclamation mark over their head, (a happy one) and they will run after you. Talk to them now and they will give you their photo of themselves.