There's no visible indication that anything is happening when you click upload, but the picture is uploading. Depending upon the size of the photo, and the speed of your internet connection, it make take a while for the upload to complete. I know when I've been uploading full resolution images from my phone (i.e., a large file) in an area with shitty data coverage (i.e., a slow network) it's taken a long time and I thought it was broken. However, it eventually worked.
Can you attempt to upload a small, few KB, image downloaded from the internet to check that it's working?
Also, can you email the exact image you were attempting to upload to
webmaster@pistol-forum.com so I can do some tests with it?
There's nothing about your account or the forum settings that should keep you from uploading an image. I'll dig through logs and see if I can see anything out of the ordinary.