If you are having difficulty uploading images perhaps you need to convert the format to Jpg or Gif. PhpBB (our board) doesnt support Bmp type files.
You can download one from this site for free. It truly is freeware with no bundled up crap or ads with it.
I use this software for all my conversion and resizing need. It can be downloaded to the desktop.
Scroll down the page for picresizer 2.0.3