Gizmodo has conducted an investigation, and they have found these images are being leaked by the US Marshalls.
A Gizmodo investigation has revealed 100 of the photographs saved by the Gen 2 millimeter wave scanner from Brijot Imaging Systems, Inc., obtained by a FOIA request after it was recently revealed that U.S. Marshals operating the machine in the Orlando, Florida courthouse had improperly-perhaps illegally-saved images of the scans of public servants and private citizens...
The leaking of these photographs demonstrates the security limitations of not just this particular machine, but millimeter wave and x-ray backscatter body scanners operated by federal employees in our courthouses and by TSA officers in airports across the country. That we can see these images today almost guarantees that others will be seeing similar images in the future. If you're lucky, it might even be a picture of you or your family.
While the fidelity of the scans from this machine are of surprisingly low resolution, especially compared to the higher resolution "naked scanners" using the potentially harmful x-ray backscatter technology, the TSA and other government agencies have repeatedly touted the quality of "Advanced Imaging Technology" while simultaneously assuring customers that operators "cannot store, print, transmit or save the image, and the image." According to the TSA—and of course other agencies—images from the scanners are "automatically deleted from the system after it is cleared by the remotely located security officer." Whatever the stated policy, it's clear that it is trivial for operators to save images and remove them for distribution if they choose not to follow guidelines or that other employees could remove images that are inappropriately if accidentally stored.
