Why does this PNG show differently sometimes?

Question

I am playing around with CodePress for a small project, and I am trying to figure out how it generates the actual numbers for the line number display.

I have looked all through the code, and I see nothing where 1, 2, 3, ..., n is outputted. However, when viewing the page info in Firefox, I see this:

Now, when I actually go to that URL in Firefox (here is the image from a CodePress example site: http://bobdawg.org/codepress/images/linenumbers.png) I just see a line with no numbers, like this:

So how in the world are the numbers being generated? Clearly they're somehow embedded in the PNG, but how?

Answer 1

You need to zoom in.

Save to desktop and open with Paint.

Answer 2

The image dimensions are 26x24010. What you see in Firefox is a zoomed out version of the image. If you click on it to view it at full size it will look the same as the preview.