Photography is both creative work and a professional service.
Every image may include hours of planning, photographing, selecting, retouching, uploading, and delivering. When someone saves an unpaid preview, they are taking something that still has professional and financial value.
This is especially important for photographers who sell individual images or digital files through their galleries.
School, sports, dance, event, family, and portrait photographers may allow clients to review several images before deciding which ones they want to purchase. If those previews can be easily captured, clients may feel less motivated to complete an order.
Screen capture protection helps preserve the difference between viewing an image and owning the final product.