Have you started your imager? Is the folder generating images?
If you followed the tutorial properly, you should have no issues. Please check over it: https://devbest.com/threads/how-to-setup-nitro-imager-for-your-cms-iis.92569/
If you still need help, please give more information as it's...
Catalogue images are usually in c_images/catalogue - I don't know how you have it setup, you'll have to find the location and edit the paths in ui-config and renderer-config.