Infringement on the Web? You Have Options . . .
Now what? You have some options - you can bill the infringer for the use or sue the infringer (after registering your image, if you haven't yet).
Thanks to the Digital Millennium Copyright Act ["DMCA"] enacted in 1998, you have another option when your copyright is infringed on the web. While the Internet Service Provider ["ISP"] is not liable for transmitting information that infringes a copyright, the ISP must remove the infringing materials from a user's website after receiving proper notice of the violation.
The DMCA has specific requirements that have to be followed exactly. The notice must: be in writing, be signed by the copyright owner or the owner's agent, identify the copyrighted work claimed to be infringed (or list of infringements from the same site) and identify the material that is infringing the work. Additionally, the notice must include the complaining party's contact information, a statement that the complaint is made in "good faith," and a statement, under penalty of perjury, that the information contained in the notification is accurate and that the complainer has the right to proceed (because he is the copyright owner or agent).
Whatever option you choose, send the message that infringement is wrong and will not be tolerated.
Take my advice; get professional help.