@Tommaso Run-cio, these sources aren't cut as well as the excellent sources should warrant. There is some snow and the edges aren't very smooth. This thread contains guidelines for what we're looking for in our cuts in terms of dimensions, snow, collars, face orientation etc. and video tutorials for each element.

If you want to give them another go yourself, I would recommend using remove.bg, which is a free online tool which removes the background to an excellent standard, for free and almost instantly.

Here's a couple of videos on how to use it, one when combined with Photoshop and another using photopea.com, which is a free online app so close to Photoshop that it has the same shortcuts, layout and icons.

If you don't have Photoshop, photopea.com is the tool I would recommend to use to tweak the draft cut produced by remove.bg. It's more powerful and versatile than GIMP and other similar tools.