GIMP is a free image editing program that has many of the features found in Photoshop. It will run on Microsoft Windows, the Mac OS and Linux. One of the features is the Selection tool, which lets you choose part of the image so you can cut or move it to a different part of the the image or a different layer. Once selected, the area is surrounded by the "Selection Marquee" which is like a moving dotted line (sometimes referred to as marching ants). Once you have finished using the selection, you want to get rid of the selection boundary so you don't accidentally alter your image unintentionally.
Deleting the Contents of the Selection
Choose the Selection tool appropriate to your purpose. Your choices, and how they work, are as follows: the Rectangle Select tool that lets you select any rectangular section of your image; the Ellipse Select tool that lets you select any elliptical or circular area in your image; the Free-Hand Select tool (also called the Lasso tool) that lets you draw a selection boundary with your mouse or drawing tablet; The Fuzzy Select tool (also called the Magic Wand) that lets you select an area that contains the same or a similar color; the Bezier Path tool that lets you select an outline using Bezier path nodes and control points; and the Intelligent Scissors, which lets you define a path around an object in your image to select the object. Your choice of selection tool will depend on the shape of your object and your confidence with the various tools. The Rectangle, Ellipse, Lasso and Magic Wand tools are easy to use. If they don't give you the results you desire, you might try the other tools if you are comfortable with their more complex features.
Draw your selection. For the Rectangle and Ellipse tools, you just click and drag. For the Magic Wand tool, a single click inside an area will select all of the area containing the same color. For the other tools, you are creating a path that goes all the way around and back to where it started. Once the selection has been defined, you will see a moving dotted line around the selected region.
To truly delete the area within the selection, select either "Cut" or "Clear" from the "Edit" menu. Clear will just delete the contents. Cut will move the selected part of the image to the "Clipboard" where you can pasted it somewhere else if you want.
Removing the Selection Outline
Select the "Select" menu at the top of the current image in GIMP. Then, click on "None" in the menu that pops up, if that option is not grayed out. This should remove the selection. If it doesn't, or if the "None" option is grayed out, proceed to the other steps below.
Take note of the tool that is currently selected and switch to a different tool. This may make the selection disappear. If it doesn't, try clicking on the "Select" menu and then the "None" option.
Save your file and close it, then open it again or close the GIMP itself. The selection should no longer be visible.