Snopes confirms: that's a mastiff. They can't confirm whether the description originates in the same place as the photo (though I personally doubt it).
http://www.snopes.com/photos/animals/bigdog.asp
I once knew a mastiff named Zeus. After an initial get-to-know-you period, he'd decide you were his pal, and he'd walk up and lean against you. This is a 230-lb dog... leaning against you. Zeus put my on my ass several times.