This kind of expression is used when you want to compare how good something is with other things of the same type. In the example above, the photos that were taken with the mobile phone probably don't look very good compared with photos taken by a professional photographer on an expensive camera. But they look better than other photos taken on mobile phones.
This type of phrase can take lots of different forms. The verb doesn't have to be "looks". It can be "sounds", "tastes", "is", and other verbs. This can be followed by "good", "well", "strong", "small", or any other adjective. Here are some examples:
You throw pretty well for a girl.
That tastes really good for something you just made up yourself.
He's smart for a dog.
Notice that the example at the top is used in spoken English. It's not quite grammatically correct because "mobile phone" is not the correct category for "photos". A more grammatically correct way to express this in written English would be:
The photos he showed me looked good for photos taken with a mobile phone.