You probably saw this in the menu at left:https://www.stampcommunity.org/sc_t...g_images.asp
After you optimized, did you download the optimized image? It will have the same filename with _OPT added to the end. Upload the "OPT" file from the edit/create box and SCF should automatically insert the link of the uploaded file.
Also, the upload thing pops up in a separate window and sometimes I lose that window behind my main window.