Copyright is virtually intangible. You can't see it or touch it. Copyright is more like a property or an attribute of an image.

As such, it is important for you to make clear your intentions regarding the copyright status of every image you create.

95% of all work that I produce is tagged, "No use without permission." However, I let the definition of the word, "permission" be a little bit fluid.
For close friends and family, permission to copy an image is almost implicit but not to sell or for commercial use.
For ordinary friends, permission is not implicit but is almost always granted if asked for. Again, not for sale or commercial use.
For anybody else, they need to contact me BEFORE doing anything with the image and the two conditions I ask for are attribution and non-commercial use.
On a few occasions, I have made electronic/digital art via computer that I have released under the Creative Commons "Attribution/Non-commercial/Share-Alike" license. Those images are clearly marked in the EXIF/metadata and watermarked in the image.

On one occasion, a friend at work copied one of my pictures and I found out about it. I wasn't mad, per se, but I did kind of poke him in the shoulder and said, "Oh, c'mon! I would have copied that for you if you asked me!"

Just because you give a picture to a friend doesn't mean you give up the copyright.