Positively identifying heat sources as human while they were immobile, squatting, and wrapped in man-blankies was a challenge with the Sperwer IR system.
I only picked up one bunch of four on a chilly December night because they were perfectly evenly spaced in a dead-straight line parallel to a major paved road. The individual blobs did not, by themselves, stand out. They appeared cooler than normal people, like a farmer stepping out of his compound to launch a midnight Liberal in his field, or wild animals, and I'd not have given them a second look had they arranged themselves randomly. I still could not say for certain that they were anything of real interest until one got up to talk to a guy hiding behind a tree some distance away.
Yes, it was an older and much more French system than what is available now, but any camouflage in any part of the spectrum is better than none at all.
One does not have to be completely hidden from view. Looking completely unimportant is adequate. We used coloured plastic sheet and woven tarps (white, blue, orange etcetera) in urban or agricultural settings in Germany to great effect, often only covering parts of vehicles. This was much better than cam nets, as everybody looks for those while dismissing "farm machinery", "haystacks", and "woodpiles" because no military person in their right mind would hide under bright orange. We would even have our neighbouring Luftwaffe RF4E Recce Phantom guys check out our position at least once per Fallex, and they never detected any of our stuff under plastic, even when it was parked right out in the open.
Don't look like a human shape, don't move, look a little cooler. There's no guarantee that you still won't be spotted, but there are generally a lot of warmish-looking blobs around. Shrubbery can help, too.
