Are you using steemit to upload, or busy.org. I have heard people complain that busy.org has a hard time with pictures. With the steemit front end it has always worked pretty simple for me, If on my computer it is just a matter of dragging the file into the posting box. If the picture is already online then right clicking copy image address and paste in the post box. The markdown code verses HTML code stuff gets a bit tricky at times, very limited HTML code, and some of the Markdown code does not work well when you use HTML codes.