This wikiHow teaches you how to make an entire image transparent when using the GIMP editor, as well as how to remove a background's image. You can do this on both Windows and Mac versions of GIMP. Keep in mind that GIMP's default export...
Method 1 of 2:
Making a Whole Image Transparent
Open GIMP. The GIMP app icon resembles a dog-like face holding a paint brush in its mouth.
Open an image in GIMP. Click File in the top-left corner of the window (Windows) or the screen (Mac), then click Open... in the drop-down menu, select an image to open, and click Open.
Click Windows. This tab is at the top of the window (or the screen if you're on a Mac). A drop-down menu will appear.

Select Dockable Dialogs. It's near the top of the Windows drop-down menu. Selecting it prompts a pop-out menu.

Click Layers. You'll find it near the top of the Dockable Dialogs pop-out menu. A small "Layers" window will open.

Select your image. Click the name of the image that you want to edit. It should be in the middle of the "Layers" window.
Lower the "Opacity" value. Click and drag the "Opacity" slider at the top of the window to the left, or click the downward-facing arrow next to it to lower the opacity.[1]
Exit the "Layers" window. Click the X in the top-right (Windows) or top-left (Mac) corner of the "Layers" window.

Click Image. It's at the top of the GIMP interface. A drop-down menu will appear.

Click Flatten Image. You'll find this option near the bottom of the Image drop-down menu. Doing so "flattens" the image, thus preserving its transparency.
Export your project as a PNG file. The default export settings will save your project as a JPG, but you'll need to change this in order to maintain your image's transparent background:Method 2 of 2:
Making an Image's Background Transparent
Open GIMP. The GIMP app icon resembles a dog-like face holding a paint brush in its mouth.
Open an image in GIMP. Click File in the top-left corner of the window (Windows) or the screen (Mac), then click Open... in the drop-down menu, select an image to open, and click Open.
Click Layer. It's a menu item at the top of GIMP (Windows) or the screen (Mac). A drop-down menu will appear.

Select Transparency. This is in the drop-down menu. Selecting it with your mouse cursor prompts a pop-out menu to appear.

Click Add Alpha Channel. You'll find this in the pop-out menu.

Click Tools. It's at the top of GIMP or the screen. Another drop-down menu will appear.

Select Selection Tools. This option is in the drop-down menu. Doing so prompts a pop-out menu.

Click Fuzzy Select. It's in the pop-out menu.
Select part of the background. Click a section of the background; if you have a particularly complex background with multiple different colors, you'll instead click and drag your mouse across it until a large portion is selected without selecting any of the part of the image that you want to save.
Press the Del key. Doing so will remove the selected part of the background. If your background was one color, the background should now be gone.
Remove the rest of the background. If pieces of the background are left over, select and remove them before proceeding.
icon next to the percentage at the bottom of the GIMP window, then click the factor by which you want to zoom in.
Export your project as a PNG file. The default export settings will save your project as a JPG, but you'll need to change this in order to maintain your image's transparent background:Update 05 March 2020
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