Hey Tomas,
I solved this issue by just adding my image to the bottom of a page (temporarily) and then copying the image's info and then pasting it to a text area in the footer widget.
there are some width limitations when you use more employ more than 1 footer area but this is a quick fix. I imagine there is a way to fix it in the template but I'm not so great with code although I am working on that.
The example I have to offer is the front of http://www.autorepair-yorkpa.com - I created the "happy customer" image and placed it in the bottom left footer box with the method described above.
I believe, if memory serves correctly, when using all 4 footer areas, an image can be no wider than 205 px before there is overlap of the footer areas
Hope this helps