Posters are pictures, made of many materials, such as adhesive, removable adhesive and so on. And photographic paper, PP paper and canvas without adhesive. They are mainly used in indoor and small format, and their accuracy is higher than that of inkjet printing.
KT board usually sticks a photo with glue on it. There is also a kind of Xuefu board, which is harder than KT board. It can be used for loading photos and pictures, or it can be directly sprayed with pictures (there is a special machine).