This is a photo taken by the streets of San Francisco. I found there were lots of very overweighted people in the country, especially women.
1. You asked "Is the sentence okay?" but you have posted two sentences.
2. A photograph is "taken by" the person who operated the camera.
3. A photograph is "of" what it depicts.
4. If the photograph is of "the streets of San Francisco" one would ask "Really? All of them?" If the photograph is of some streets in San Francisco, then OK, but I suspect the photo would probably be of a street in San Francisco, unless the person with the camera was in a high place. It may be enough just to say that it was taken in San Francisco.
5. There is no such word as "overweighted". I think you mean "overweight", "fat" or "obese".
6. True or not, many Americans will be offended to see you calling them fat in your example text.
7. "Photo" and "lots" are informal. "Photograph" and "many" are better for formal or standard writing.
8. The jump from San Francisco (a city) to "the country" is a rather abrupt change of scale. It might be better to say "the USA" (if you had seen everywhere in the US, unlikely) or "where I was". Best of all, avoid making sweeping pronouncements.