I have some issues with clients uploading to big images. Mainly because they don't know what a big image is. They have no understanding of px and mb. 

So on the image field, I can set a custom warning to the client. If they try to upload a to big or small image in mb they get a warning. Also if its not the right amount of px in width or height. Trying to upload a landscape image in a portrait box. (yes people even tries that).

I would like to set the parameters on every one, because sometime they need to upload a full page image and sometimes a 50x50px img. 

If I can link to a site in the warning, where they can crop and make the image smaller, that would be awesome.