Sorry to resurrect this old post, but I found Miliardsto's reply to his own issue unhelpful for figuring out what could cause imagesearch to not work on some PC's. As I was running into the same issue trying to automate some Citrix windows that do not contain controls, but only images. Hopefully this helps someone with the same problem.
Check the monitor's Display settings and make sure the size of text, apps, and other items is set to the same percentage as when you took the screen shot of the image file you are searching. I ended up creating 2 files for every image being searched. One at 100% and the other at 125%, as our company laptops default to that percentage. Now imagesearch works on all our PCs.