You can take pictures in whatever outfit you chose. I'm personally taking mine in jeans and a shirt just because I have so many.
My only suggestion is that when you do take your pictures to keep the outfit consistent so you can personally see changes. It would be kind of pointless to take a photo in normal fitting jeans and a normal fitting shirt then the next week you take a picture in baggy jeans and a loose shirt. You wouldn't see the difference.
This also may apply to the color shirt or pants you chose. (Remember black is more sliming than white.)
