How to exclude camera from recent App list? (long-press Home Key in Galaxy S 2)
I don't want it to appear in the Recent app list since it has traces/image of last captured image.
You can remove it from the list by just swiping it off. I don't know how to permanently remove it from the list, though.
Judging from the fact that you are seeing previews of recent apps, I'm assuming your SGS2 is running Android 4.0 (or ablove). I don't believe you can exclude apps from "recent" list out of the box.
This might be one of the few legitimate uses for the Task Killer kinds of apps. Basically if you set the task killer to always terminate the "Camera" or "Gallery" apps, they should stop appearing in Android's recent apps list.*
*[Correction]: The above statement turned out to be incorrect on Jelly Bean (Android 4.1). Task-ending an app does not remove it from the "Recent" list.
I just tested it while writhing those steps and it's working if your phone is rooted. If you need a method without root, Just ask me and I will try to do some test.
You can use Tasker! When you launch an app with tasker, you can specify to exclude the app from the recent apps.
You could create a button that launch the camera app in excluded mode.