some products dont do a very good job of reducing image s to fit the resoluion for a slideshow doe not do a very good job , one reason is that a camera is a square image eg 4:3 video works mostly on 16:9 .
one way you may try is to set the images to max 720 wide or 560 high
then stretch the canvas to 720x560 .
this worked for me, and proshow and pictures to exe are designed for slideshows. both are available as a trail , i would advice you to try them and compare the 2 different programs with your results from windows 7
i hope this help