Images are only published to Shopify on the initial publish, thereafter they aren't syncing between Vend and Shopify.
We will send the main image only when you first publish the product to Shopify. Any additional images need to be directly imported into Shopify.
If you remove the main image on Vend that won't remove the image from Shopify. You'd have to manually delete the main image on Shopify.
If you remove the main image on Vend and upload a new one, that won't override an existing image on Shopify or sync to Shopify.
If a product on Shopify has images but the Vend product doesn't then uploading an image to the Vend product won't override the images on Shopify.
Pulling the Shopify products into Vend won't bring the images.
If these products were already published, you will need to unpublish the product, delete on Shopify and then republish it to show all the images.