zxing_cpp.rb | ZXing Ruby bindings for the ZXing C library

I'm trying to bulk scan some jpg files with barcodes on them. I've used the ruby bindings for the c++ port of xzing. When I have this file:

scanned by the Web-Version of Xzing (https://zxing.org/w/decode.jspx) everything turns out fine. When I try to scan this one in ruby (using https://github.com/glassechidna/zxing_cpp.rb) nothing is recognized. I already tried cranking up the contrast, but it did not help. It's not my ruby setup because it works for loads of other nearly identical codes. The only thing I can think of is any difference between the Java version and the C++ port, but this is absolute poking in the dark, I've started using zxing just today. Could anyone get this code recognized in ruby? Thank you very much.