An image may not show up in dlvr.it's Queue for a number of reasons. The most common reason is that the image is not sized appropriately for our systems to see it. Our image size requirement is 400x300 pixels.
If your image is sized appropriately, it may not be tagged appropriately. You may not have the image setting to detect your feed images, or you may not have Open Graph tags on your pages. The most effective way to make sure that images are posted to all platforms correctly is to use Open Graph tagging.