Large images (greater than 1280px in either dimension) are automatically downscaled, which may remove transparency from PNGs.
Images uploaded to StashDB will be downscaled to no greater than 1280 pixels in either dimension. Due to an old bug, PNGs may be converted to JPGs when downscaling. This means that studio images might lose any transparency they may have if it’s over 1280 pixels tall or wide. While this bug has been fixed for most users, it may still affect the occasional file. You may need to manually downscale transparent images to fit these size requirements before uploading them to StashDB if it becomes a problem.