I had to send pictures to a host to show the lack of cleaning done prior to our arival. There's two ways I can see. Assuming you now have a phone number add them to your WhatsApp and send pictures that way. If you've tken the on the same phone - no problem. If not, send to yourself by email, open and send from your phone via WhatsApp.
Second, in the phone app, there's a camera icon to the bottom left (if yoyu've been messaging them alresdy), it allows you to send or take pictures either take a picture or use the ones you've emailed youtrself.
Finally and its a bit late for the person wanting to send a staircase picture....why noit include one in your listing? If one guest has asked for there's a good chance someone else will.