Using Social Media

[Dan Friedman]

I have a client who want their mobile app (for iOS and Android) to:

(1) Take a picture (a selfie).
(2) Put a watermark on the photo.
(3) Post that photo to the user's Facebook, Instagram and/or Twitter account with a specific hashtag.

Step 1 and 2 are easy.  Step three, on the other hand... not so much.  Can this be done?  And, if so, can anyone point me in the right direction?

Thanks in advance,
-Dan