I've reused photos also. One thing to note: When you use a photo the first time, it's saved in your Photos section. If you upload it again for a different hub, that one is also saved in your Photos section. If you upload it once and then decide you want to edit it some more before actually publishing, both the original and edited versions are saved in your Photos section. This makes for a pretty long Photos section! My advice is to choose from there, instead of uploading it again when you want to reuse.