Start with adding photos and write necessary descriptions or notes immediately for each one of them.
Most essays are aimed to depict events, objects, emotions and ideas through writing.
Photo essays are quite different from such papers because they consist of many images sorted by a topic.
Make sure that all your images are directly related to the topic of your essay, serving its informational and rhetorical purposes.
The written part of the essay must support and explain images.
Thus, you have to write your descriptions and notes according to the message of each particular illustration.
For example, if some image is funny, you have to point out what is funny about it, in the text.
Some photos may seem quite useful while you’re preparing and collecting the material, but as soon as the major part of your essay is done, they may turn out to be not the best choice regarding the general context.
In this case, it’s good for you to have more photos so that you’ll be able to replace these images with the better ones.
Thus, don’t be afraid to take too many photos before you print them.
Take your time and select a couple dozen best images from among a hundred.