How to Mask an Image in Keynote

Masking an image in Keynote allows you to easily change its shape, creating visually interesting effects. Here's how to do it:

1. Simple Image Masking: Cropping and Resizing

The simplest form of masking is cropping your image to a desired shape.

Double-click the image: This reveals the mask controls. The initial mask will be the same size as your image. On a Mac with a Force Touch trackpad, you can also force click (press firmly) the image to access these controls.
Resize and reposition the mask: Use the handles around the image to adjust the mask's size and shape. This crops the visible portion of your image, effectively masking the parts outside the selected area. Click Done to finalize the mask.

For more complex shapes, you can use Keynote's built-in shapes to create a mask:

Select your image: Click on the image to select it.
Choose "Format > Image > Mask With Shape": A menu of shapes will appear.
Select a shape: Choose the desired shape (e.g., oval for a circle, rectangle, etc.). The image will now be masked to the shape you've selected. You can then resize and reposition the shape to adjust the mask.

For truly customized masks, use your own shapes:

Create a shape: Insert a shape from Keynote's shape library. This will be your custom mask.
Position the shape: Place the shape over your image. Ensure the shape is covering the desired area you want to show.
Select both the image and shape: Click and drag to select both the image and the custom shape.
Right-click (or Control-click): A contextual menu will appear. Select the option to "Mask" or a similar option (the wording may vary slightly depending on your Keynote version). The image will now be masked by the custom shape.

Image formats: While Keynote supports various image formats, PNG files often work best for preserving transparency in masked images.
Editing the mask: Once you've created a mask, you can always adjust it by selecting the image and modifying the mask handles or the shape used as a mask.

Remember to save your work frequently. These methods allow you to create various visually appealing masked images within Keynote.