changing header for Elegant Grunge

I want to change the header for Elegant Grunge. I want the header to be a photo that I’ve uploaded to my ftp site. I’ve incorporated the blog title and description into the photo, so I don’t want any additional text to show up. Will this cause a problem with search engines? Should I perhaps have the text that usually goes in the header somehow invisible?

Can anyone show me how I modify the code to do this?

Thanks!