Open that picture. Click the button titled "Share", which can be seen in the gray bar above the picture. Copy the address of the picture that shows in the "Direct link" row, just under "Link". Start a new Reply here, and click the little icon that looks like a picture. It's the third one from the right, and if you hover your cursor over it, "Insert Image" will pop up. When you click the icon, another window will pop up. In that window, click the "From URL" tab. When that tab opens up, paste the address (URL) that you copied before. Uncheck the "Retrieve Remote file..." box, unless you want your picture to be small, like this:
A3_F132_ED-3_C73-4_B6_B-977_F-_F71_D358_DC186.jpg
Unchecking the box posts your pic in all its glory:
Boom...