On the website it’s the same. Click the pattern you want to put the photo, in the top right corner there will be a option “add photo” and just repeat the steps. Hope this helps!
@vscodonut if you’re on the app, click on the pattern you want to post the photo on. Next there is a plus sign on the top right corner of the screen, press it and it will tell you to add a photo or video. Press photo and you can either take the photo or pick it out a photo you already took on your phone by pressing the Library option.