"A very common request is to create a page of thumbnails images for a website with links to full-sized images."
This should either read "...create a page of thumbnail images..." or "...create a page of thumbnails..."
You put an 's' on thumbnails.
The tutorial itself looks good and seems simple enough to follow. Some of your pictures are a little grainy though, and could maybe be higher resolution. If you're worried about page load speed there is enough information on the page to warrant splitting it.
One comment I do have is that you've used capital letters for your file and folder names and the tutorial is in a folder called Irfan View, with a space between the words. This is translated into the URL as .../Irfan%20View/... with a whole lot more capitals. Although it shouldn't cause issues, it may. Just thought I'd mention it.
The tutorial looks good though.