Everyone loves to see a picture of themselves...right? RIGHT! And if they see a picture of themselves sitting on their desk, they're going to be curious and they're going to open the card.
Try to make the photo relevant though...say they were featured in an article or there was some big news about their company. Or you found them on LinkedIn and they said something really cool.
Then in your message, reference it..."Congratulations on the article!" or "That was a great blog post."
They'll know you took the time to learn about them and they'll be interested in you!