When on your visits view, click on the cog wheel on the top right-hand corner to see the visit actions. Choose Attach media. You can take a photo or choose exiting photos at your photo library. After you take the photo, you'll see two buttons at the bottom of the screen: use photo and retake. Choose appropriately. 

You can attach several photos to the same visit. To see the list of photos in a visit, click on the paper-clip top right-hand region of the screen:

Then you can see a list of all your photos in that visit and visualise them. You can also delete them by pressing the bin icon.

When you're done, click on the top right cross icon to exit this list.