When you are in the media pannel, just do a drag&drop from windows to add a new picture. When you click on this new picture, you have directly the concerned URL, as shown. There’s also an edit function, its only useful functionality is to resize or crop an image, but all the picture software do this, paint included.
The standard redlab picture has a width situated in a 200-400 pixels range. If you need more space, just create a miniature that you can click on for a larger picture.