When sending a new message there are two quick options available.

To swiftly send a picture from Messages, tap the Photos icon from the iMessage App Drawer. If you don’t see the App Drawer, tap the App Store icon to reveal it. You can then choose a picture from Recent Photos or you can scan through and send an image from All Photos. Just tap the picture and it will be added to your message thread. 

For even more photo-sharing options, drag up on the Photos iMessage app to reveal a larger interface, which will include a selection of Sharing Suggestions taken from the Photos app.