Best way is to use <img src>to bring in the image in the header.php and then use CSS to position the jpeg. If you do not understand what these are, then you need to study HTML and PHP and the apply to WordPress. Its not hard, but you are going to need some basics.
If you want to use different pictures on different pages, you can do this by category, custom fields, is_home, etc……but you are going to need to use a If/else conditionals using PHP.