Using phone screen as a barcode

I believe the reason your phone does not work is because the screen is not reflective.

What happens when the barcode is scanned (usually) is that a laser dot is swept across the bars very rapidly (thus it appears as a line).

As the dot hits the black and white parts of the image the laser is reflected into a sensor more or less, creating a pulse which a computer can read.

From here you can probably see why your phone dose not work. Although the barcode appears similar to a code printed on paper, as the laser hits the screen it does not reflect more or less light, so the digital pulse is not generated.

Note that the pulse occurs in time, based on the speed of the laser dot so your red and black image will not work either.

What could theoretically work is if your phone could rapidly flash the pulse that would result if a laser were scanning an actual barcode. Unfortunately your phone screen probably cannot change colors fast enough, and you would also have to know the scanning rate of the laser.

I don't suppose you bring an e-reader to the gym though? Because that would work the way you expect, since it reflects light, and doesn't just produce it.

There are some barcode readers (especially QR code readers) that can read a phone screen reliably. I believe these use a camera to read the code and not a laser. These will usually be a box with a clear window that you place the code against.

Bar code readers can read phone screens

You can get apps that store cards on your phone (e.g. Stocard) and they work pretty well; at least as good if not better than a printed barcode on a scrunched up grocery bag.

I suggest that your photograph is distorted or not clear enough - these apps generate the correct bar code from the numbers and don't suffer from this problem.