Isn't that just like distributing object code? The more detailed image could (in some respect) be considered the source code.
Source code and object code are qualitatively dissimilar, and it is nearly impossible to understand or change object code. By contrast, a larger image and a smaller version are qualitatively similar: a person can directly see both, and can edit both with the same tools. So the analogy is not a good one. The smaller image is not as desirable as the larger one, but it can be entirely free.