Something to be aware of when sending an image: Apple Mail may mangle the image you sent, recompressing it while greatly reducing it in size. One consulting client kept sending me screen shots that were so tiny so as to be unreadable.
It wasn’t obvious what the problem was, so here is the answer: check thecontrol in the mail window. Consider that with the new iMac 5K and a 3:2 image, an image has to be around 12 megapixels to fill the screen pleasantly.
Alas, one more thing to waste time, as it did with me and my client. The problem with OS X and iOS is that dozens of such things creep into the interface, making it more complex—full of land mines for simple tasks. My iPhone regularly tricks me into doing something unexpected; in iOS land I suffer since I don’t know it as well and I am no teenager.
What I have not yet figured out is that I have sent full size images to some people, who then receive a mangled downsampled version (my outbox has the full size image, so full size was surely sent). In that case it seems as if the mail server of the receiver is mangling the image.