Moding how guest visitors access galleries

I have installed Gallery 3 for a friend of mine who is a photographer and he wishes to password protect certain galleries. Not a problem as I have done that before but he also wants the gallery to be visible in the front page of the site but the cover image to be replaced by an image which shows the album to be password protected (e.g. grey image with padlock)

When a guest clicks on the gallery then they will be prompted for the user login. If the user is already logged in then the gallery will be visible as normal

Can anyone offer any pointers or know of a freelancer who is interested in taking on the project?

regards

Ian