For interest check, I think detail outline of the plot is necessary, a few question here and there work well you're still catching interest. It' only when you move into discussion of how things will play out and how to go about them that your moving into a more OCC type discussion.Personally, I won't use images in an interest check, unless the image is very important for the cause (basing a role play off that very image). Some people may do it because it catches the eye a little better over just text. I personally like to use images at the top of my IC posts, as a kind of reminder of who my character is. It was a habit from the pro-board sites I wondered onto for a while in my break on the guild a few years back. I really does help when it comes to multiple main characters in one IC post. 

For the images I use, I do create them myself using a program called Paint.Net. it's free since I'm a cheap ass person, but it works for my needs. It's rather easy to use and has helped me make basic images and some more complex images where I've had to use the layering system.

I think that covers just about everything.