When the user downloads a new image or captures one using the camera, the gallery app will get updated to show the new images.
I need to be notified
You may want to look into adding these to your filter as well:
com.android.camera.NEW_PICTURE
com.android.camera.NEW_VIDEO
android.hardware.action.NEW_PICTURE
android.hardware.action.NEW_VIDEO
The android.hardware.x actions are the "official" current broadcasts, but the com.android.x ones are sent by Samsung devices and older versions of Android.