These extra photos are what Zen Cart calls additional images, there's a switch in Admin to control their display and they are attributed to a product based on the filename, see -
https://docs.zen-cart.com/user/image...images-feature
Don't forget that Zen Cart requires three different sizes of images - small (for product listing pages (among others)), medium (for product info pages) and large (for the enlarged images on product info pages). The plugin mentioned - Image Handler - will automatically create these and just needs a large image uploaded. Note that Image Handler calls these images 'additional images', not to be confused with the extra photos discussed above.
I think here you are talking about responsive images, that resize depending on changes to the screen size. That is controlled by your template which is itself responsive so, assuming it's a decent template, I don't think you'll have an issue.
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