There is a huge market for good photographs which is steadily being cornered by some of the big players (like Getty Images). Giving away photographs is a way to get an audience and if one can collect some tips on the way, that is a great plus. An angle for photographs which is used on a few sites like https://www.dreamstime.com and even for graphics like https://thenounproject.com/ is to give away a smaller size image and charge for larger size images.