I am using the script straight out of your documentation and example including "format" => "png",
as you described.
Output comes as data:image/png;base64,
with a long string of characters that has to be captured in javascript because it is contained in a windows DOM widget, then stripped of the prefix and saved, which I never completely got. In short, if you want to save the image in it's current format, it is a lot of work to convert to a saved file.
Here is the output straight off the PNG on your example page:
<krwidget widget-name='' widget-type='koolreport/barcode/QRCode'><img src='data:image/PNG;base64,iVBORw0KGgoAAAANSUhEUgAAAKoAAACqCAYAAAA9dtSCAAAACXBIWXMAAA7EAAAOxAGVKw4bAAAEVklEQVR4nO3d227jOBRFQXvQ///L6acBBtOJW7ZJkcuqeg5kRtoxc3jT/evr6+sGm/tndQPgCEElQVBJEFQSBJUEQSVBUEkQVBIElYRfR3/wfr/PbMdQIybbHv2+313/2Z+frfK8jt4b36gkCCoJgkqCoJIgqCQcrvrrVlblsyvwKywpHhJUwy8/34Pd2nm7NZ+Xrp8EQSVBUEkQVBKmVf0ji4hCVbtj0fSM3Z/XZYannr15I2/2iEUs9T+Ed+n6SRBUEgSVBEEl4TLF1O5V7X9dvXD6jm9UEgSVBEElQVBJEFQSBJWEywxPvbIC/5lhqNlrCa4+ZOUblQRBJUFQSRBUEi5TTI0qRkprBj7JtKB6CGPNvp+7Py9dPwmCSoKgkiCoJAwppj51em/27/XT9We/I6D4vC4zPPXI7H339um/T9dPgqCSIKgkCCoJiqnb84XN7J/nT4eDuvtc8N+cccb+Tq+erD+v/9P1kyCoJAgqCYJKwuFiamXl+qlTkLN3Hew2NfxOgWd46oHd/kB2a8+ZdP0kCCoJgkqCoJKQKKZWFQxXm9NfsaPh6EjA23P9s+eyz1g5v9OwzOywrDrV8N3fS9dPgqCSIKgkCCoJibn+n+zYpu+sOknwmTUAI9syY9H2kOGpFSvVdwtppZ2rvJsRXT8JgkqCoJIgqCQsOc1vp23Fo5SKplJb/5VYlPKd3d7EN/taZ6wlWHV/jtD1kyCoJAgqCYJKwv3r4H/FxUpxllULtj/x+sNX+L9i1Vn3V97//ql0/SQIKgmCSoKgkjC1mFq1L75SOFXauYNpK/x33Bc/83M/+TWPOywK0vWTIKgkCCoJgkpCduH0K8XIiAKmVATNbOvZ92GboM5eUV/f6nK7XXsthK6fBEElQVBJEFQStimmfnJGdT/z1LuRdi94ZpoW1DMe8qodBDPb85PZoxbPXuPs0wt1/SQIKgmCSoKgknB61T/yn+3ZOwhWvMlu5XWedeaoyPbDU7fbmh0EVx4Keoc393FpgkqCoJIgqCQkiqkKBdg8h4M6aihit+uM+uzd1hg8a/cdELp+EgSVBEElQVBJOFxMlSra3Q4sW3HvZhdHl93XXzdyjtvagz/p+kkQVBIElQRBJUExNcjKnQuz7dCeaWf4zzbrVYavXv8VM6v7VecqzKLrJ0FQSRBUEgSVhGlVf2lh8Cr1ff1nMjz1wMzdCFcI10i6fhIElQRBJUFQSVBMPVA5238ns6a2BfU2pipf+ebB2dfZga6fBEElQVBJEFQSFFO3+Wf7f+oowZmFmaA+sNMK/LPflPe3zz779EJdPwmCSoKgkiCoJCimHqifwrdqB8GM+zYtqKUhmZlz6ztatQbgnfuj6ydBUEkQVBIElYQhxVR1Me5os3cE1O/zd+23wv9Nq+bWX/ncEX8IK9cSHKHrJ0FQSRBUEgSVhPtXZd6PS/ONSoKgkiCoJAgqCYJKgqCSIKgkCCoJgkrCb0wluurXvo9yAAAAAElFTkSuQmCC'></krwidget>
I am looking for an option to write directly to a file such as qrc-my-link.png
then I can save the file on my server, and call it from database whenever needed.
Is standard practice to simply output for viewing every time it is called? I am giving my customers the option to choose one of three sizes to use in their advertising.