GIFs are 8-bit 256 color palette limited for entire image (animated or not), hence degradation will be very noticeable due to each image having photo type source and having to share the same restricted color palette. There is simply no way around, it's a technical limitation of the format itself. And Flash, thankfully, is not allowed in signatures. Your option is to heavily reduce color range, i.e. to make backgrounds greyscale. Possibly adding interlace effect too. Otherwise ain't going to work at all.