Google has added a feature on Gmail that makes it easier for people that back up photos from their smartphone and tablets on Google+ to share through e-mail. You can insert pictures and photos directly into e-mail, resize them with the message, and share them with friends and family. You would need to grab the photos that are pulled through the Auto Backup feature on Google+.
You will notice the feature under Insert Photo on Gmail:
You can resize the images when it is inserted. It supports the ability to drag the corners to find find the size that you want.
You can sign up for the Google+ Auto Backup feature here.