From the below snippet we can check the list of running applications and check whether your application is in foreground or not.

ActivityManager actvityManager = (ActivityManager)
this.getSystemService( ACTIVITY_SERVICE );
List procInfos = actvityManager.getRunningAppProcesses();

boolean appFound = false;

for(int i = 0; i < procInfos.size(); i++)
{
if(procInfos.get(i).processName == "com.android.camera")
appFound = true;
}

if (appFound)
Toast.makeText(getApplicationContext(), "Camera App is running!!!!", Toast.LENGTH_LONG).show();
else
Toast.makeText(getApplicationContext(), "Camera App is not running!!!!", Toast.LENGTH_LONG).show();

the above snippet shows your camera application is running or not.