Turns out VisualStudio was bugging out and didn't show me the Install System.Drawing.Common until restart :(

Was able to solve this with:

Bitmap bitmap = new Bitmap(front);
bitmap.MakeTransparent(Color.Black);
bitmap.Save(front);
BitmapImage bi = new BitmapImage();
bi.CreateOptions = BitmapCreateOptions.IgnoreImageCache;
bi.UriSource = new Uri(front);
this.Front.Source = bi;