I've worked on my website, and have been trying to design my logo. My sister, who went to school for graphic design, told me that you can't use a photo for a logo or as part of a logo.

My question is, how true is this? is there a set rule for making a logo that states that you can't use a photo as part of your logo or is this not so. please help me with this. thanx for your help. Any opinions and suggestions are greatly appreciated.