An ISBN-barcode has to be well readable. You get the sharpest result if you work with vectors (instead of bitmap like JPG, PNG or GIF).
The most programs in which you can create a thesis cover also support the vector format Encapsulated PostScript (EPS). That’s the reason to create your ISBN-barcode in EPS-format as well.
Create an ISBN-barcode in EPS-format yourself
Enter your ISBN and press ‘Create ISBN-barcode’.
This generates an EPS-file with your ISBN-barcode.
You can import this file in Adobe InDesign or Scribus and use it for the cover of your thesis.
This generator is based on the generator of Terry Burton .
Here you find barcode-generators that also can export to other formats: