Zebra printer: printed images blurry

My customer recently bought Zebra GK420t printers and wants to print barcodes with them. The barcodes are JPEG files with a resolution of 3000x5000 pixels. The DPI is 203x203 and the images are 1-bit.

The barcodes are printed in Firefox. Because the barcodes only need to be about 150x250 pixels, I included them this way in the HTML-page:


UPS is doing this the same way with their labels to keep a good quality image. When I print the labels with a laser printer they just look fine. But when I print them with the Zebra printer they look blurry. I also tried printing it in full size with the Zebra printer and they just look fine then. Below are the results I scanned:

Zebra vs Laser:
URL
http://img854.imageshack.us/img854/3869/zebra1.jpg

Zebra fullsize:
URL
http://img208.imageshack.us/img208/6259/zebra2r.jpg

Does anyone know what I'm doing wrong? Why is the result on the Zebra printer blurry?

Why not simply print it full sized? You say it looks fine printed full size...do that.