Log in to ebay.
Go to seller's listing and on the same line with the "Description" and "Shipping and Payment Tabs", all the way to the right, is a link to "Report Item". Click on that.
When you get to the reporting page, under Report Gategory select "Copyright and trademark".
Under Reason for Report, select "Images or text copied from your listing".
Under Detailed Reason, select copied pictures or text.
You can take it from there