Yeap you can use a wi-fi card like eyefi. But they send the signal when you take the photo.
Depending on the camera there are some adapters that could send live view images. For example: http://www.nikonusa.com/en/learn-and-explore/article/h4spl2xm/shooting-wirelessly-with-nikon-digital-cameras-and-wi-fi-adapters.html