Professional photographers will seek a model release for pictures they take. The distinction is that individuals captured in the image are or can be recognized. In a picture of a group of people, think a large crowded scene, it shows people but few are recognizable. So a model release is not practical or necessary. A picture of two women walking down a street, those women can be recognized by themselves and people who know them. The 'perv' pictures and video's are posted and it is possible thoses images contain features that can identify the women. These can be faces, tattoo's, birth marks scars etc. Many photographers will take what is called 'stock' photographs. These are uploaded onto websites and newspapers, magazines, marketing companies will search them looking for images that portray what they are selling or looking to illistrate. Posting recognizable pictures without a release is illegal, at the very least the images would be removed. Most websites would do so if asked. A few years ago I went into the SFU downtown bookstore, while looking around I found a bookmark. It showed a long line of Graduates walking down the steps to the Convocation Hall; in the middle of the shot was me. Very recognizable because of my height and the shortness of the persons standing infront and behind me. I showed it to the cashier and she as have others I've shown it to agreed it was me. Had I wanted to I could have required the picture be removed. I didn't because it's a laugh.
