I have found as we are switching our website to Square that if you want photos to show for the online Variations, you have to upload the Images (as opposed to simply dragging and dropping).
On the Squareup side you can simply drag and drop the Images into the Items and into the Variations and it also puts those into the Image Library.
Online Square does not provide access to the Image Library in Squareup nor does it have a drag and drop feature on the add Variation Image screen.
It would be fantastic if either the Variant Photos from Squareup transfer directly to Square online variants or that you be able to access the Image library from both sides.
Thank you for your attention!
Square Community