take your pic with a digital cam or a regular camera.
scan the developed photo from the regular camera, or download the digital pic from the digi-cam.
open your fav photoediting program to make sure you are not over the size limit. you can crop away unwanted areas of the pic and or reduce the resolution( usually the 'dpi' (dots per inch) section has a number indicating res. 72 is about as low as you'd wanna go IMHO. scanned & digi-cam pics can be quite large(300 dpi)) of the pic to achieve this.
save it as 'whatever name you want.jpg' file in a folder you'll remember the location of on your hard drive.
go to the gallery and open a new thread. where it says 'attach file' you hit the browse button and go to the location you saved your picture at. select it and it should show up when you submit your thread.
there you go. clear as mud.