Pinterest doesn't seem to be able to find images within slideshows. Please fix this - it's a big part of marketing (in general). Is this also the case for search engines?
You can optimize images for search engines by defining Image Properties. Defining informative file names and alt text always helps in getting images indexed faster with relevant keywords that describe it. More about image publishing guidelines here - https://support.google.com/webmasters/answer/114016?hl=en.
Thanks,
Vinayak