Say Cheese and Die - Again! is a novella written by R. L. Stine. It was first published in 1996 and was the 44th book in the original Goosebumps book series.
Description[]
To prove to his English teacher, Mr. Saur, that the camera he found in the first story is real so he can raise his failing grade on a class assignment, Greg Banks goes back to the abandoned house to retrieve the camera – and finds that it still works. But after accidental snapshots, he finds as Shari becomes skinnier and skinnier, Greg grows fatter and fatter.