Those photos were first publicly released
In our VK group. The story of them is that one guy contacted me, said he has a video from one of Valve's closed presentation for Source engine devs, were they showed one of some old HL2 build with the unseen gravity gun model. The presentation was called "Making game trailers" and took place during the GDC '06. He showed me the video in skype and also made those screenshots for me, but didn't let me to release the actual video.
I made a remake of this video recently: