it's either a glitch or just a problem demon fox hasn't fixed yet.
you're only going to be able to use a picture on the internet(or yours if you upload it to the internet), when you find the picture you want to use you need to right click it and "copy image location", then click paste in the area where you put a web address, you can also do this in posts by clicking she small icon that looks like a a portrait(a mountain with a sun over it).
