For those of us who use an avatar and especially those who post a logo rather than a picture, the standard background provided by the forum operating system may not be pleasing. So it was with my heraldic shield JPEG.
In the GIMP I edited the avatar by adding an Alpha Channel, selecting the background, clearing it and exporting as a PNG.
No doubt other editors can do the same thing ...
And if you don't want an avatar, like me, simply create an image with all pixels transparent and save as a png.
Jpeg doesn't support transparency.
In Ps/PSE put the avatar image on a normal layer, not background layer.
Select the background you want to make transparent and click Delete.
The deleted pixels will be assigned as transparent pixels.
If you are using a background layer type then the deleted pixels will be set to whatever background colour is set at the time.
