I believe this appears in your root "/files" directory, under a numbered folder (ex. /files/1908/). Of course, the numbers would be different for you, and there will likely be multiple levels (ex. /files/1908/4405/, etc.).
I could be wrong, but that seems to be where most generated or uploaded images are stored, including thumbnails. So, my best bet would be to look around in the root /files/ folder.
I could be wrong, but that seems to be where most generated or uploaded images are stored, including thumbnails. So, my best bet would be to look around in the root /files/ folder.