A photo has to be attached to a post with text in. Even a full stop will do.
Type in the box where you normally do for posts, then look under that box for a + sign with "attachments and other options"
Hit the + sign, then under where it says Attach, hit the "choose file" button. Your device will then get you to decide where to look for the picture, and which one to use. For multiple pics, hit "more attachments" and choose more pics.
Your pictures will not show in preview, but their names will show in the attachments box.