Identify and ignore placeholder image uploads

[teolemon]

What

• Some apps upload or have uploaded placeholder images in the past.
• While the nocode solution is to ask them to stop, it would be nice to have our own checksum based solution to ignore images, that could be limited to some specific users to avoid wasting resources.
• Identify and ignore placeholder image uploads
• Example: https://world.openfoodfacts.org/images/products/590/078/300/0455/front_en.29.full.jpg
• https://world.openfoodfacts.org/product/5900783000455/heinz-tomato-ketchup
• https://images.openfoodfacts.org/images/products/474/002/960/0749/1.jpg

Part of

• Better detect image reuploads #7054

[github-actions]

This issue is stale because it has been open 90 days with no activity.