There’s an advanced Image Filtering option built into the WordPress Custom RSS Feed Plugin that lets you choose what should be included in a feed based on image requirements. For example, you can choose to include all Posts with the ‘Sports’ tag that contain an image that’s at least a Full HD resolution (if that’s one of the custom Image Sizes you have defined in WordPress for example) or classified as Large by WordPress by default. Or you can choose to skip Posts that do not contain an image.
This helps you meet requirements when using the RSS feed to syndicate content to an external source. You can also use this feature to specify which Image should be included if you have different variations. If you’re automatically generating a variant of an image that contains a watermark, this would likely be saved in WordPress as a Custom Image Size (see this Plugin if you’re unsure what we’re taking about) which you could specify would be included instead of the regular Image included in the Post.