I am trying to overlay an ice texture over my render. The image is mostly white so it should work with transparency. At the moment I am stumped on how to archive this. Help is very much appreciated. 
Take rendered image to compositor as an input node. Take texture to compositor as an input node. Mix together, send to compositor output node.
Okay so I have tried many combinations already. I have tried every single mix function in the drop down. I would not have posted if I didn’t already try a bunch of other things.
Perhaps you could post a screen grab or demo blend file? It should be quite easy.