I've got an dynamic HTML page that contains a QR code that is generated dynamically and embedded using <img src=data:image/png:....>. I had been testing the page by generating it with specific arguments and verifying that it matches the output I expect.
I'm now discovering that the embedded image is not as fixed as I expected. The PNG format uses zlib compression, and for Python12.3, and Windows and Linux are using different versions of the zlib library. (1.2.13 and 1.2.11, respectively). I have two correct but different compressions of the identical source bits, and the resulting PNG representations differs. The resulting dynamic page now longer matches exactly the output I expect. (The windows version now compresses to a few bytes shorter.)
I can easily verify that both pages contain the identical source, except for the images. Is there a easy way of taking the byte strings that are the PNG representation of the generated image and the image that I expect and confirm that they are the same?
Answer
netpbm is a set of image manupulation utilities, including pngtoppm, which converts a png image to the raw, uncompressed ppm format. You can use that to see whether two png images are the same or not.