According to the article they want to upload and process "selected pictures from your camera roll" to make suggestions.
Now the definition may vary, but the camera roll is probably the list of images on your phone (which the app accesses when you pick an image to post), not a list of pictures you already posted privately...
Now the definition may vary, but the camera roll is probably the list of images on your phone (which the app accesses when you pick an image to post), not a list of pictures you already posted privately...