A method, system and computer program product, the method comprising: obtaining a multiplicity of images taken by one or more overhead capture devices overlooking a body of water having a surface; detecting a person depicted in at least some images from the multiplicity of images; determining for images in the images, whether the image depicts the person in substantially vertical position in the at least some images said determining performed upon one or more characteristics extracted from each image; and subject to determining that the person is not in substantially vertical position in the at least some images, taking an action.