There are two shortcomings of GIF: it can only store 8 bits per pixel, and it cannot be transparent. There isn't any cure for the second one, but the first one can be sometimes improved by using a good dithering algorithm (ie. save it with an app which has a good dithering algorithm).
Are you speaking about the two film strips at the top? The problem probably is that the displayed photos have way different colors, which makes choosing a good-fitting palette of 256 colors problematic. It might be better if you didn't use blending for switching the images, as this creates yet more colors to be encoded.