Way back, I did some experiments to resize pixel graphics (black and white), while retaining the 1 pixel line width, but correctly resizing things that had "volume".

I did it like this:

• Cut the image in 1 pixel horizontal strips.
• Go over the line, adding object start-X and end-X pixel color.
• Resize it by multiplying each start-X and end-X with the factor (2 or 4, 3 looks very ugly).
• Reconstruct the lines into a new image canvas.

As a 1 pixel width item will have the same start-X and end-X value, it will retain the 1 pixel width. And things that have different start-X and end-X values, will get streched as if normal...

edit: Then, you need to rotate the image 90 degrees, and do it again to strech it in the Y axis.

However, what you want is the inset function in inkscape, not a perl program, as your source is a bad quality jpg, instead of a pixel perfect png.... (so dithered pixels get in the way of the above mentioned algorithm... it gets confused)