If you want people online to ID mushrooms from pictures, it's important to get pictures of where the gills meet the stipe (stem), what the bottom of the stipe looks like after you've picked the mushroom, and the surrounding area (just like the pic you posted).

Also take note of how they smell. Some are sweet, some are earthy, ... there's an impressive range available. Another attribute to note is if they burst into crumbles when thrown at your friend, or if they're stringy when torn in half. Spore color is also good to know. In some situations, it's the only identifying factor between look-alikes.