I’m an Android developer recently moved to Windows Phone 7 development. In Android, we were able to share pictures generated in our apps using a common (generic) sharing context menu which lists applicable (installed) social networks and apps that can take photos as input. (as in the image attached to the question.)
In Windows Phone 7, apparently, Android Intent-BroadcastReceiver mechanisms are not implmented. My problem is, how can I share a picture generated in my app (let’s say my app only takes pictures using camera) on Facebook, Twitter, Mail etc. without using their APIs (because it is not really easy to integrate 3rd party apps and increases app size etc.)
Thanks.

There isn’t a built in way to share images from within your app.
If you save the image to the phone’s medialibrary then it can be shared using any installed, registered app via the pictures hub, as per http://msdn.microsoft.com/en-us/library/hh202966(v=VS.92).aspx
Update for Windows Phone 8
Windows Phone 8 includes the
ShareMediaTaskwhich does allow your app to share image files.