I don't know how you attempted, but the way I do it is by using a web based picture site, like photobucket.com.
When the picture is there I click on the picture then when it appears in its own window look to the right. Under "Share Links" there is a "Direct" box. Clicking on that copies it.
Then when posting back on the AHA site, when you click on the picture icon which is above the text box it produces two square bracketed objects. put your cursor between those two innermost brackets, right click and select paste. That will paste that picture address you just copied off of photobucket or wherever.
That's it!