@Hasjasja Are these sources pre-cut or did you remove the background yourself? A lot of the Xamax cutouts you posted have a lot of background snow/partially visible pixels so the background wasn't removed properly. Care needs to be taken to ensure that there's no snow in your cutouts, just cropping and resizing a pre-cut image isn't enough. Example of this, duplicating the layer a few times so it's more noticeable:

Cleaned cutout and brightened the shadows @mons