I don't understand the technology of the filter tags.

What I noticed, and I'm not sure if that is the same for all people, is that when I insert an image in the TinyMCE editor with drupalimage(img_assist), the image is a frame with a little camera at the center. Once I publish it, the image is shown as normal.
Why isn't the image shown as normal when editing? Is it due to the filter tag technology? Or I didn't install correctly my modules?

I noticed the same thing with GMap.
Is there a place for more documentation?

Thank you.
Ronan