Sure you can. If you've got webspace included with your internet service, put it there, and post the link with the [IMG]http://someurl[/IMG] tag. If you don't have such webspace, you can use services like
this one to host your images, and post the link as described above.
If all else fails, you can use the 'attach file' facility, and just attach the pic that way, or hell, just do a rough ASCII 'drawing' of it.
[edit] If you're saying that the file-attachment facilities don't allow for your file format, try saving as/exporting to an image. Programs like Visio, etc have this ability, and if you're doing a pen-and-paper version, just snap a digital pic or scan it in, like
crawforddavid2006 suggests.