In the past, when I went to Photos and selected a few images, and after sharing them via email, the previously selected images still had checkmarks in Photos. That prevented me from accidentally sharing the same images again. Lately, the checkmarks are no longer there and I have a bear of a time knowing which images I have already shared. This is not a problem when the images are all distinctly different but I often have a bunch of very similar images. Does anybody even know what I'm talking about?