Illustrator is a versatile vector graphics application, but you can't use it to edit raster images -- like JPGs, GIFs and bitmap files. For example, you cannot cut a raster image you have imported into a document so as to use only a part of it. However, Illustrator does provide a way to get the same result.
Load the image you want to use in Illustrator onto your computer.
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Click on the desktop shortcut to start the Illustrator application. Select "File" from the menu and choose "New." In the dialog, enter the size for the document and click "OK."
Select the "Pen" tool from the toolbar on the left. In the options at the top, turn on the "Fill." The color you choose doesn't matter.
Use the "Pen" tool to draw an outline around the part of the image that you want to keep. You can drag as you add each point to better define the lines between the points.
Select "Object" from the menu and choose "Clipping Mask." From the options, choose "Make." Only the part you wanted to keep will now show.