you don't need any picture; you can assume what it can do by looking at the OP. I haven't added anything graphically significant to the game that would warrant a screenshot other than the ability to look on the other side of a door.
People like pictures. You can take pictures of every add-on. For example: picture of the build, picture of the door, picture of what part of the build you see when using it.
The usual add-on browsing goes like this:
- open topic
- look at pictures
- no pictures? can't be interesting, leave
- read text below pictures