This scenario is not supported by defaul Media Selection control.
The easiest would be to specify Validayion rule against your field like this:
All you need to do is to implement this custom macro rule ValidateImageSize(mediaUrl, minWidth, minHeight). So in macro rule you need to:
- get MediaFileInfo object by URL (you can cut image GUID from URL and find by GUID)
- check media file width and height against your borders, that's it!