There is a lesson learned here. You need to have a contract when you license an image to someone. Get yourself a copy of Tad Crawford's excellent book, Business and Legal Forms for Fine Artists. I think it should be in every professional artists' library. Here's a quote from one reviewer on Amazon:

"Business and Legal Forms" has the documents you'll need, such as copyright transer forms, publishing contracts and stock listing forms for your creative work. His descriptions are very helpful. Of greatest practical use, though, is the included DVD containing MS Word documents of all of the forms. If you're just getting started in fine arts, or even if you have been working a while, you need this book!"

You can't make assumptions about what other's intentions are. That is why you need legal documentation, even for seemingly simple transactions amongst friends. To get some ideas on licensing, you can learn much at: http://www.porterfieldsfineart.com/newartists.htm. You can also get great free information from www.salestipsforartists.com. Another good source is NOLO. It has some free information and lots of legal advice and forms. And, Michael Woodward's  Art Licensing 101 is another valuable resource as is the General Art Business forum on www.wetcanvas.com.