If you would like to make a black-and-white picture with an object colored then here is how this can be achieved via GIMP. Here is an example of what will be achieved.
Select the object you are separating from the background using a selection tool (the “Intelligent Scissors Select Tool” lets you select a freehand border and uses edge-recognition algorithms to better fit the border around the object. Use this when the subject is complex but distinct enough against its current background). Once you have selected your subject successfully, use Select → Invert. Now, instead of the subject, the background is selected.
To make a black-and-white background while keeping the subject in color:
From the main menu select Colors → Desaturate. In the dialog that opens, cycle between the modes and select the best-looking one, then click OK.
