There will be time where you're unable to scan QR code using image injection. This issue occurs could be caused by the injection process that's unable to locate the center of the image.
Prepare the QR code with blank spacing on both left and right sides of the image. This spacing will ensure the injection process be able to locate the center of the image and scan the code.
This is similar to preparing a check for use with image injection as detailed at Creating images to be used with check scanning apps.
Creating images to be used with check scanning apps