Still a beginner in Blender and modelling a bottle. I managed to place the label on the Glasbottle with a Mix Shader Setup. Happy that i found the solution for my myself at first - but then i then noticed: Not really. The Bottle was half the label and the label was half the bottle (glossy, reflections).
I asked a friend and he just plugged the alpha from the Image Texture Node into the factor of the Mix Shader - and all was fine and perfect. The Bottle was glas, the label was not.
I asked him: why. And he said: Dont know - i know this from a website. So i still wants to know: Why is this the solution. Why is this working? Is this the only way or are there other solutions?
Here are two images with and without the alpha plugged in to the factor.