Perhaps the thing I most often use the Gimp for is to remove a background. It is quite simple and fast once you are familiar with how to do it. This tutorial will focus on just the basics. It will show how to remove a single color background (this is the easiest way to remove a background).
(Here is a video I made if you would prefer to view how it can be done.)
I just did a quick Google search for "random clipart." Here is the image I ended up using.
|Here is the image we are working with. On the right side of the window, you will right click the layer and "Add Alpha Channel."|
Once you have the image you want, you will open it up in the Gimp. The very first thing you will want to do is "Add Alpha Channel." You will get this option by right clicking on the image layer (found on the right side of the Window). Near the end of the list you will see "Add Alpha Channel." Click on it. (There is a possibility that this is grayed out, in which case the Alpha channel has already been added and you don't need to do anything.)
After we have selected the tool, I like to go to the tool options and enable "Feather edges." Feathering edges is what gives us a nice smooth object. If we do not feather the edges, the edges of our object will be pixelated and will not look good.
Feathering edges gives you an option to adjust the radius (this determines more or less how smooth the transition will be). A general rule of thumb is that the larger your image is, the higher you will want the radius. Because the image I am editing is quite small, I turned the radius down to 3.
After we have adjusted the radius, we can now select the background. This works very well because the background is a consistent color. If you are looking for clip art online, it is wise to be mindful of the existing background. You can save yourself a lot of time if the background is a consistent color.
You can now see that the object is selected. The black and white dashed lines (marching ants) represent the area that is selected.
In this picture you can see a closeup of the hand. Notice how the marching ants go around the black of the hand. Many of the pixels still have a dark yellowish color to it though (this is a feathered edge. The transition between two colors). This would look a bit weird if I put this image on a white background. To get rid of this, I want the selection to be a bit closer/tighter. To do this, I will press and hold the shift key while I press the selection again. When you press shift, you should see a + sign next to the magic wand (fuzzy tool). This means that it is expanding, or adding to the selection.
Using the shift key (adding to the selection) is especially important when you have a background that is not a consistent color. This allows you to select all the ranges of colors.
Now that I have added to the selection, you can see that the selection no longer includes yellow pixels.
If you want to remove the selection to look at your image without the marching ants/outline, you can go to "Select" and "None" (or just press Shift+Ctrl+A).
We now want to export the image (Shift+Ctrl+E).
Make sure you export the image as .png (or gif). If you export it as .jpg the background will be white. JPGs do not allow transparency.