if you used photoshop, make new layer first then delete the background layer. Save it often or so, because what if you forgot to save it as .psd and you saved it as .png instead
also, i checked your image's hotlink; obviously it is in .png and you may either forget to delete the background layer or not.
If you are planing to post it as .png or something with the transparent. imgur support it kinda, but not over [X] size which changed to .jpng. sometimes, it doesn't show the transparent background and changed it to black, grey, or white whatever it showed up on imgur hotlink
you can read it here
deviant art might be best in my opinion if you got [X] size