It is only okay if you got the consent! That's the way it is.
Look...if someone steals your recipes and photos and posts them, it's wrong and you may report. But how sad for them. Originality is what makes us unique and someone who copies is just sad!

I personally have used two photos from google and have not mentioned it's source, it's just to show the place i ate in, and i didn't have taken a photo teh day i ate there. But for me this is okay, what do you think? I n the end the pictures of their food were mine and i was making advertisment for that eating place.