In chapter 11 of Harper Lee's To Kill a Mockingbird, Atticus provides an example of a simile when he greets nasty Mrs. Dubose:
Good evening, Mrs. Dubose! You look like a picture this evening.
Comparing Mrs. Dubose to a picture (Atticus's compliment to the older woman) is saying that she looks beautiful—perhaps not in the sense of beauty as we know it, but in the sense that she is composed, posed in a manner that deserves being captured by an artist's (or photographer's) eye. Scout, of course, cannot imagine "a picture of what" that Atticus is referring to.
Another simile is found after Jem destroys Mrs. Dubose's camellia flowers. The kids return home and sulk around until Calurnia give Jem a biscuit with butter, which he shares with Scout. She notes:
It tasted like cotton.
The biscuit, we can assume, is flavorless and dry in her mouth, much like cotton would be. The reader might assume that her reaction to something that sounds delicious may in fact have a great deal to do with Jem's crazy behavior that not only destroyed the flower garden, but also Scout's newly acquired baton—which Jem broke in half.