When you upload colour/custom images for variants or products in the group, you must follow certain constraints. An alert will be displayed if incorrect input is added. Let's have a look in detail.
If you are uploading the custom image using
Add from URLorAdd filemethod, it must be a publicly accessible URL. You can use the URLs for the images added in Shopify.The URL must be an image of the format JPEG, PNG or GIF.
File size must not exceed 512Kb
The following alert will appear in the popup if you have added the incorrect format.
Refer to the following articles:
To upload colour/custom image for Shopify Variants.
To upload colour/custom images for Product groups.