QR Code with Logo

I played around with adding a semi-transparent layer to the QR code for my business, Excellence in e-Education. It works for me, but I’m curious whether it the logo messes up the ability of some scanners to read the code. I use both the Barcode Scanner and QuickMark apps on the Droid to scan QR codes. Works with both of them. If you make the logo too dark, it won’t work. If you make the logo too light, you won’t see it. Sort of trial-and-error to get it just right.