Why won't an image of a barcode scan but a real bar code will?

I’m trying to send someone a barcode from a software that generates barcodes. To do this, I took a screenshot of it using snagit. The only problem, no matter what the resolution or size is, is that a barcode scanner won’t read it. If I print directly from the barcode software it reads fine. I don’t get it. I played with size, resolution, substrate and nothing works. Please help!