In the early days of photography, the exposure time was a severe restriction with a studio portrait often requiring 5-10 seconds when the person could not move. To overcome this, the model would rest on supports and sometimes had clamps behind their head to make sure it did not move.
But there was a second reason why early photos seemed to look like paintings. Hiring nude models for several days was expensive. But by taking photographs and using them as the basis of a painting significantly reduced costs. It became a very lucrative business for a many photographers.
However, they soon found that they could also sell these images to a wider public, still claiming these were intended for artists, and therefore could not be prosecuted under obscenity laws. Hence sales tended to be under the counter.