GiMP is a free graphics manipulation software that gives you tools and effects comparable to those you can create using programs like Adobe Photoshop. Feathering an object's edges is an easy way to help integrate an object into the background or to tone down a harsh outline. Feathering an object's edges is a simple task that shouldn't take the user more than 15 minutes of dedicated time, and will be familiar to anyone who has used the lasso tool to create and manipulate selections within the image.
Open up the image in question in GiMP by selection "File" and "Open."
Select the object by using the "Lasso" tool in the toolbar on the left part of the screen. Click and hold the mouse down to begin the selection, dragging the cursor along the outline of the object. Drag the cursor all the way around the object until you've formed a complete outline, and then release the mouse button. Note the checkered path marking the selection you have just made.
Feather the selection by going to the "Select" menu and choosing "Feather." Increase the radius of the feather to create a "softer," larger gradient, or decrease the radius to create a smaller gradient.
Right-click on the selection and choose "Select inverse" from the drop-down menu. This will select everything but the selection you just made. Now hit "Delete" on your keyboard to remove everything else. This will delete the outline of your object along a gradient, feathering the edges.