I want to know is there any way to use the input of an external camera connected with android tablet using USB into my application that is running on that tablet.

I would suggest you to try this one android-webcam Also this will be helpful to you developer.android.com/guide/topics/connectivity/usb/accessory.html

I've succeeded to get this project to work with my webcame connected to my Android tablet: https://github.com/saki4510t/UVCCamera. However, the issue is that it relies on native libraries and comes with many samples undocumented. I am myself still looking for better ways.