The image, captured in April 2016 by an intelligence-reconnaissance plane, was included in a classified briefing video on UFOs shown to multiple US government agencies.
The briefing video describes it as a 'short clip of an unidentified flying orb that appears to have a metallic shine on its surface', and shows the strange object flying over the city of Mosul in northern Iraq, with the background of the shot showing the streets below.
Lack of focus at 1500mm focal length (very powerful zoom, maybe 1° FOV), suggests it's not near the ground.
Specular highlight suggests a metallic sphere, such as metal-coated mylar.
Not falling suggests a balloon.
The reported motion suggests a parallax illusion, but verbal descriptions are not much to go by.
But it also looks kinda like a water drop.