This is kinda confusing, so read carefully.

Watch the episode where Malcolm goes to a sleepover at Stevie's house. In the little opening sequence thing, the family is at the portrait studio. They're all off doing different things (Malcolm/Reese fighting, Dewey getting in other people's pictures, etc.)

Hal is trying to convince Lois to use a different backdrop for the picture, and he likes lonely beach instead of the tree backdrop that Lois wants to use. When Lois gets really mad and she tells everybody to sit down and take a picture, you see Hal pull down the tree backdrop over lonely beach that he was looking at.

Hal pulls the tree backdrop all the way down, but when Dewey sits down, look behind him and you see the lonely beach backdrop behind him.