I've just been gave a Samsung S3, and it come with Android 4.2 (so I cant apply this guide) So I post this question, Please guide me how to take picture using volume key with Samsung S3 (Android 4.2)!?
just visit this link, it's worked for me http://indahpurngrm.blogspot.com/2016/04/how-to-use-volume-key-to-take-picture.html?spref=tw
In summary: root your phone and install Xposed Framework and then the Xposed Additions module. From that module you can intercept the volume up key and make it take a screenshot.