Let's be very careful with the use of photographs "as text" in the elementary school. Yes, it is true that the visuals will help students build more connections and create more schema when applying sound to symbol to concept.
However, it is imperative that you ADD the text TO the picture. Many studies in the teaching of language show that it is a necessity to put text to picture in order to acquire the entire semantic value of a word. This is so because students can quickly connect spoken words to visual concepts, but many are ready for "the next step" which is to decode the sound and symbol and produce it themselves.
Therefore, never ever please show a picture without offering students the opportunity to build schema through text. It is very very important!
A picture is worth a thousand words, or so they say. When the direct text is not given to the student, and they are instead forced to interpret, as they would be with a photograph, then this has a number of educational benefits. They must use focus, imagination, association and inference skills to get textual meaning from images. These are fairly high level thinking and learning skills to use in a classroom.
Some students are visual learners, and respond more effectively to visual stimuli such as graphs, videos, photos, and charts.
On the down side, photos will elicit a number of different responses, so if he information or skill you want them to learn isn't flexible, then pictures won't be as effective at getting all students towards one goal. Science and Math, for example, would have harder time using images than say English or History, because the content is so much more specific, and less open to interpretation.
Some students are not visual learners, and look for more specific direction from the teacher. So while it is beneficial for some, it is detrimental to other students.
I would say there are lots of benefits. Especially in the study of English, all students need to be taught how to analyse all kinds of text that they are going to encounter. Clearly, photos and visual images are used a great deal in the whole area of advertising, and so this would be a key area to employ the use of photos in teaching. All English programmes should include a topic on media forms such as advertising so that students can understand how photos function as texts and how they are manipulated and used to "sell" products or to give a certain message. Decoding such texts is a vital life skill that I really feel would disadvantage our children if they didn't learn it.