Depending on the country and if you are shooting under a contract (employment or otherwise), you generally would own the copyright to what you shoot, but this does not mean you are free to do anything you wish with the photo. I'm not a lawyer, but the stock photo agency Almy claims a property release is required with pet photos for commercial use, I would expect photos on cards for sale to be a commercial application and subject to this requirement. Note, this is an Almy requirement and not necessarily a statement of the law, it's still worth noting.
http://www.alamy.com/stock-photography-rel-guide.aspOne lawyer's opinion
http://www.danheller.com/model-release.html#8.3The best thing your friend should do is discuss it with an attorney that practices in this field.