We discussed and debugged the issue already on IRC some time ago. It seems that the camera App from HTC does something different which doesn't trigger the instant upload. Tested with HTC Desire S (Android 2.3.5, HTC Sense 3.0) and the ownCloud Android Client 1.3.8

EDITED by @davivel
SUMMARY on 26/02/2016

The problem: third party camera apps often fail to broadcast the Intents with action android.hardware.action.NEW_PICTURE and android.hardware.action.NEW_VIDEO that the OC app listens for to know when a new picture or video was taken.

The probable solution: keep alive a FolderObserver on the official folder where pictures / videos are stored to know when a new picture or video was taken.

Main references on this:
#6 (comment)
#6 (comment)
#1059

To keep in mind:

• There are third party camera apps that don't use the official DCIM folder to store their captures; let's ignore them first.
• Android Services are not granted to be there forever; this could result in problems to keep the FolderObserver alive; risk is low, since that's the approach already used to observe kept-in-sync / favourite files, and our experience in this point has been fine.
• The app keeps too many Services. We should tend to merge them in a different architecture, with a more uniform synchronization model. Internally, the concept of 'instant upload' should evolve to 'automatic addition, later sync'.