Rollover text with grey gradient on Ishimoto gallery

I'm trying to achieve an effect like this:

http://www.amysherald.com/

With text that appears on a grey gradient on rollover on the main Ishimoto gallery. I found a couple pages that describe how to do this, but on the above website the gradient covers just enough of the image to make the text easier to read. The gradient changes size depending on what text is displayed on the image. I haven't seen anyone describe how to do that, can anyone help me figure it out? Thanks!