1. You can glue a common substrate (which will be the same for all images) and differences (i.e., additive) - ship separately, an "extra" on the substrate, receiving the desired image.
So - will reduce significantly the total size of the images if they have a lot of similarity and one size "cloth", because the "appendage" is the only unique difference of this image from all others in the current slider.
2. A common "substrate" and "add-ons" - ship as a single stream of binary data and restore to a normal image on the client, putting the result in the slider.
To do this, You have to report all images in the tree, where each node of the "tree" contains auxiliary data. You can use a Huffman Code
"Substrate" is the longest common portion of the image that is present on all images (coordinates X,Y, and RGB color).
The "add - ons" - slight differences between the images with a common "substrate" (the branch of the tree).