Have you uploaded it to SSD gallery? If you have, just go to that layout and right click and select "copy image location". Then you come to this thread and in your comment space there is a yellow button w/ a mountain on it up top. Click that button. In the space given, right click again and hit paste and then hit the summit button.
Then you can submit your reply on the thread and it is there.
Another tip: when I go to my image to copy it's location I like to make sure it is the bigger size (just my preference) so I click on the picture I want and let it be the only one on the page from the gallery and THEN copy the image location. If you want the smaller size, like the thumbnail size in the gallery, then just copy the image size from that location. Does that make sense or did I just confuse you?