Between olives I've been served at restaurants as a starter and various brands of olives I bought in supermarkets I have found that the ones in restaurants often taste much better. In particular they are often less salty, less bitter and more buttery in taste.   Is this a bias on my part, maybe because I tend to be more hungry when I go to a restaurant or are they actually better. Are there particular varieties of olives  (eg. specific region or method of preservation or preparation) that taste like the ones in restaurants? Is it that they are fresher at a restaurant?  EDIT: I'm referring to plain olives here, not a processed. The kind you get as a starter, sometimes with some bread on the side. In particular mediterranean or middle eastern restaurants serve them that way. 
In comments you note that you last bought a jar of green, pitted olives in brine. Those tend to be much saltier than the versions served as a mezze in Mediterranean and Middle Eastern restaurants, in part because the restaurant versions are usually whole and thus have less surface contact with the storage brine. They're also fresher; restaurants that go through larger quantities of olive can afford to purchase higher-quality olives that haven't been sitting in their brine on a shelf somewhere for months (or years).  Olive variety may also be a factor. The picture you've provided looks closest to me to a Castelvetrano olive, which have a very mild, almost buttery flavor.  This mildness comes from its processing, which is close to the preparation of the black California olives familiar to Americans. They're washed in a lye solution, which flushes the bitterness of the fresh olive, and are then rinsed to remove any traces of lye; they can then be brined for a short period of time, but they're typically much fresher and less salty than other olives. I know a few chefs who like serving them as a starting course specifically because they're not overwhelmingly salty.  As others have suggested, you can seek out similar higher-quality olives in bulk at boutique grocery stores. You'll have to pay a bit more for the privilege, but the other advantage is that such stores are usually happy to let you try some of the varieties before you buy. 