Need help baking, "No active image found in material slot"

I have unwrapped my model using Smart UV, and created an image texture for each of my materials in the node editor. But, when I try to bake, I always get this message, "No active imagine found in material slot (0) for object “[OBJECT]”. In the log, this message pops up for every single mesh I have made for my model. Im not sure what a material slot is either.