Picture to Icon can make transparent icon easily and quickly.
If your source picture is PNG, 32-bit BMP or GIF format, transparent icon can be made directly without any adjustment. And 24-bit PNG  or 32-bit BMP support alpha channel, the icon will be semi-transparent, which supported by Windows XP, Windows Vista and Windows 7.  
If your source image is JPEG or BMP without transparent format, picture to icon still can make transparent icon easily. With the similarity transparent adjustment, similarity flood color fill, wonderful transparent icon can be made quickly. The following screenshot show you how to adjust transparent of a jpeg icon.

Create transparent icon with picture to icon