texture won't save

Hi, I am trying to texture a face model that I am working on using projection painting, but every time I save the file and reopen it again later, all of my texture work disappears. Can anyone tell me how to save the texture on the model in Blender? Thanks.

Save it as file from UV/Image editor OR ‘Pack as PNG’ to save into .blend OR File>ExternalData>Pack intoBlend.