The above leaked photo reportedly came from a 2018 document prepared by the Unidentified Aerial Phenomena Task Force (UAPTF), the US defense department's group that investigates UFOs. From The Debrief:
The Debrief learned of the existence of the photograph from a defense official who has been verified as being in a position to have access to the UAPTF intelligence reports. Additionally, the same two officials with the DoD, and one from the U.S. Intelligence community with whom we previously spoke, confirmed that the leaked image is the same photo provided in a 2018 intelligence position report issued by the UAPTF.
The photo itself is said to be considered "Unclassified and For Official Use Only," however, because the image and accompanying report were shared on a secure Intelligence Community network, the officials we spoke with would only acknowledge it under strict conditions of anonymity. Prior to any agreement, The Debrief did verify these sources were in fact in positions within the U.S. Intelligence Community and under the authority of the U.S. Director of National Intelligence[…]
According to officials The Debrief spoke with, the photo appears to be the same as one referenced in our previous reporting, described as an "unidentified silver 'cube-shaped' object" encountered by military pilots as it hovered motionlessly over the ocean. It appears evident that the image was captured by the backseat weapons systems operator of what appears to be an F/A-18 fighter jet.