You have to copy the URL with JPEG/PNG/JPG in the end. The file extension. Paste it. Save the settings. Reload your page. It should work.
Otherwise do one more thing. In reply to this comment, you can see following line.
Insert images by dragging & dropping, pasting from the clipboard, or by selecting them.
Click the selecting them link and upload your desired image in reply. Upon completion, you will see ![Caption] (URL) in the editing area. Copy the URL inside () and paste the link in profile settings box. Save.
I hope it will solve your problem. I will update this guide soon and include even more information.
RE: How to Add Profile Picture & Cover Photo and Set Up Steemit Profile - Newbie Steemians Guide