My client asked if there was no insulation in the wall.
Often during a home inspection my client follows me around when I do a thermal image sweep to check 
for insulation issues or roof leaks. They like looking over my shoulder and listen to my explanation of what they are seeing.
Sometimes I show them ghost footprints on the wall, but that's another story.
In this house we entered a bedroom and there was a long cool spot on the wall.
My client immediately asked if there was no insulation in the wall, and that was why there was the cool line from top to bottom.
I said that could not be the case because it was an interior wall and
it was 85F outdoors.
And then I pointed out the cool line was beside the receptacle on the wall, which you can see at the bottom toward the right in the image.
Knowing what was going on, I said, "See the cool area that looks squarish? There's a reason for that. Come with me."
So he followed me into the next bedroom.
"Look at the wall," I asked, and now look at the thermal camera.
It showed the same patterned line down the wall, which ended right at the HVAC register. Since the AC was running you can clearly see the cool register in the image. It was this same pattern that was evident in the other image above. You were just seeing it from the other side.
My recommendation: thermal cameras see temperatures in the form of tens of thousands of individual pixels of information which it then converts into an image. With software I can choose a color palette which best describes what is being looked at. In this case you are looking at a cool duct and HVAC wall register in two bedroom walls, and seeing the same thing from both sides. Knowing what you are seeing and correctly interpreting the camera information is the crux of thermal imaging during home inspections. And that takes training, and practice, practice, practice. And the ghost who stood on the wall above sure has great arches!
Jay Markanich Real Estate Inspections, LLC 
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560
