Sorting pictures by beginning sound is an excellent way to help students develop phonemic awareness, alphabetic principal, and writing skills. It is also wonderful for English Language Learners because pictures help vocabulary development. Pictures can come from any resource, magazines or books that are published for that purpose.
But pictures are useless unless you can find them when you want them. So, take 13 legal sized envelopes, fold them or cut them in half and bind them on a binding machine or with book rings. Label each half of an envelop with a letter of the alphabet and load with pictures. They are within reach whenever you need them!