I created an image by altering a photo. I want to move it from my computer into the BTS site so others can look at it, but I'm not sure how to
"upload (?)" it. . . .
It's not particularly good; I did it with the windows paint utility.
A good solution would be to use ImageShack. Upload the image to their free server and copy the url they give you.
Then paste that url with the required BBcode into whatever forum you wish.