Photographs from Adventist history may be found on the ASTR image collection (http://images.adventistarchives.org/), as well as in the Adventist Digital Library (http://adventistdigitallibrary.org/); the White Estate photo collection (https://ellenwhite.org/media/image-gallery/1); the photo collections at the Center for Adventist Research at Andrews University (https://www.centerforadventistresearch.org/photos/); the Loma Linda University Digital Archive (https://cdm.llu.edu/digital/); as well as at other Adventist university and college libraries, often in their special collections or heritage collections.
If you use a historic image, please make sure to properly note where you found the image, as that will give proper credit to the archives or library which holds the original item, and it help others to find the photo in the future.