The QT4 logos were designed by Bethan Tovey-Walsh. They are released under a Creative Commons CC0 license.
The plain version is available in SVG or in a selection of PNG sizes:
(The image background is transparent, the same images are shown against both the light and dark backgrounds.)
The shaded version is available in SVG or in a selection of PNG sizes:
The outlined version is available in SVG or in a selection of PNG sizes:
