how to “call back” images from posts in the recent-posts sidebar

hi
I’d like to build a “visual” menu, by using the images that I will insert into each post, so when the post is complete all I see in the “recent posts” widget or sidebar (or everywhere else) is not displaying the text of the title, but the main image that I have inserted instead.
so when I’ll have several posts, all I’ll see are thumbs of the main image of each post. and then I can click one post and I go to that post page.
I hope it’s clear…

is it possible? and how do I do it?
thank you