Sometimes, the lines between architectural and real estate photography get a bit fuzzy. To me, architectural photography involves, amongst other things, specialized equipment, waiting for or creating the right light and much more scene control. However, I’m aware that there are some photographers who believe the lines between the two zig where I believe they zag. From the client’s point of view, if they get images that meet their needs they don’t care how we photographers label them.
IMHO, the most defining difference between the two categories is how an image will be used. If it’s to appear, for instance, in print, like Architectural Digest or Southern Living magazines, the work is architectural. If the image is to appear online to sell real estate, the category is real estate.