Say you wanted to insert this picture...
If you right
click this image, and then open 'properties', it will give you the image 'Location'.
So in the Signature box in your 'Profile' menu, you just copy in the image location address, and surround it with this...
immediately at the back end.
You then have to click on the Submit
box at the bottom of your profile page, and the image should then appear under all your posts.