Need aspect ratio to match still images

    I create slideshows from still images using CS6 that are then put on DVD and uploaded to vimeo.  The problem I'm having is that I wind up with letterboxing on the sides (not top/bottom) since the aspect ratio isn't correct

I've looked on google and I can't figure out how to create a custom project that has an aspect ratio that matches the still images instead of trying to force them into video aspect ratios.

Is this possible?

Thanks.