Translation:This photo looks good.
It has no meaning by itself here. It's a counter word, and is only required for grammatical reasons. When you count objects, like 照片 (photos), a counter word must be placed between the number and the noun. This is also true when you refer to objects with the demonstrative adjectives 这 (this), 那 (that) and 哪 (which), as well as some other adjectives, like 上 (last) and 下 (next). The particular counter word used depends on the object being referred to. There are also a few nouns which don't require them at all.
Acknowledging that "hen" can be used to connect the noun and adjective OR mean very, the question becomes how to tell the difference. Here I would have guessed didn't require it and wonder how very good looking is distinguished. An objective way to determine this beyond case by case or just know from experience would be much appreciated. Thanks.