Google just keeps making this better and better. For some people, I tell them to sign up for Google+ simply for the backup features of their pictures. And now Google has made Gmail able to attach pictures that were backed up from your phone or tablet. So if I take a picture with the HTC One (M8) I can then jump over to my laptop and send an email and attach that picture. Just as easy as can be. We could already see our pictures in Drive, and we could also attach items from Drive, but now we are cutting out the middle-man, so to speak, and making it much easier to attach pictures.
To insert a picture, just tap on the pictures icon to insert one as you'd usually do. And all your backed up pictures should then populate that popup box. Just select your picture, choose whether you want it inline or as an attachment then tap on insert. Just as easy as can be. Google is quickly becoming the premiere place for storing your pictures. As you get unlimited space at 2048x2048 dimensions - or if you want full-size pictures you've got 15GB of free storage to store those, and they give you all kinds of photo editing tools as well as auto-enhancing your pictures, which is always great.
The feature doesn't appear to be rolled out quite yet - as it's not available in either of my Gmail inboxes - but we should see it hitting everyone's inbox in the next few hours or so. If you have it available in your inbox, be sure to let us know how you are liking this new feature in Gmail. I think it's a great idea and I can't wait to see what else Google does to integrate Google+ into the rest of their services. It'll definitely make things easier around here, when forwarding screenshots and such to other writers on the team.