From the Start screen, swipe left to display the apps list.
Alternatively, tap All apps (located in the lower-right; may require scrolling to the bottom).
Tap new (located at the bottom).
From the "To" field, enter a 10-digit mobile number.
Alternately, enter a contact name. As the name is entered, a matching contact may appear and can be selected at any time.
Alternately, tap the plus symbol (located in the upper-right), tap a contact then select the appropriate mobile number (if applicable).
Repeat this step as necessary to add additional recipients.
From the "type a text message" field, enter a message.
Tap Attach (located at the bottom).
Tap Photo or video.
Tap the appropriate folder (e.g., Camera Roll, Saved Pictures, etc.)
Tap the desired picture(s).
Tap Accept (located at the bottom).
Tap Send (located in the middle, above the keypad).