Do you want a thumbnail on the post when only seen on the front page, or a thumbnail for every post and seen on every post?
A simple way of having a photograph on the front page but not in your post is to use the EXCERPT box on the Write > Post screen. Put your photograph in there, and then change the index.php file where it says
the_excerpt() and you will get the explicit Excerpt that you did, which would be the photograph.
That's the simplest way. There are also plugins and things that add photos to categories and things like that. Am I close to what you want?
I do this on my site.