Paint.NET is a free open-source application for photo editing. It has many of the advanced features that you might find in expensive photo editing programs, but since the developers are all volunteers, the software is free. Outlining an object in Paint.NET is a simple process you can accomplish in a few moments. The result is your original object with an additional outline around it.
Open Paint.NET and then click on the "File" menu and select "Open." Browse to the location of the image you want to edit and double-click it. The image opens for editing.
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Click on "Tool" in the menu bar and then select "Magic Wand." Click on any part of the background that you don't want and then press "Delete" on your keyboard. Repeat this process until the background is completely gone and the object that you want to outline is the only thing that remains.
Click on the "Layers" menu, and then "Duplicate Layer." Locate the Layers window in the lower right corner of the Paint.NET screen. Uncheck the top layer, and then click to select the bottom layer in the list.
Click "Adjustments" and then select "Brightness/Contrast." Slide the "Brightness" bar all the way to the left and the "Contrast" bar all the way to the right. You will be left with a black silhouette of your original object.
Click "Effects," point to "Blur" and choose "Gaussian Blur." Slide the bar to toward the right until the blur level is seven or higher. Click "OK."
Re-check the box next to the top layer in the Layers window, and you'll have a black outline around the original object.
Increase or decrease the amount of Gaussian Blur to change the size of the outline.
Before you apply the blur to the silhouette, use the "Fill" tool and fill it with a different color if you want the object to have a colored outline. For example, use a yellow fill to make the object look like it's glowing.