After you add a photo or graphic to your document, you can crop it, remove parts you don’t want, and make adjustments to its background and exposure.
You can hide unwanted portions of an image without modifying the image file.
Double-click the image.
The mask controls appear. The default mask is the same size as your image.
Tip: To display the mask controls on a Mac with a Force Touch trackpad, force click the image (press firmly on the trackpad until you feel a deeper click).
Use the controls to frame just the parts of the image you want to be visible.
Click Done.
To mask an image with a shape, select the image, choose Format > Image > Mask With Shape, then choose a shape. Drag the handles on the shape to adjust its dimensions.
Use the Instant Alpha tool to make parts of an image transparent. This feature is useful for removing an unwanted background or color from an image.
Select the image.
In the Format 
sidebar, click the Image tab.
Click Instant Alpha.
On the image, click the color you want to remove, then drag slowly over it.
As you drag, the selection grows to include areas that use similar colors. Click and drag multiple times to remove multiple colors.
Remove all of the color (even in other parts of the image): Press the Option key on the keyboard as you drag.
Add a color back to the image: Press the Shift key on the keyboard as you drag.
Click Done, or click Reset to undo all your changes and restore the image to its original state.
Select the image.
In the Format sidebar, click the Image tab.
Use the controls to make adjustments:
Exposure: Changes the overall lightness or darkness of the image.
Saturation: Changes the richness of color in the image. Dragging to the right makes the colors richer or more vibrant.
Enhance: Automatically adjusts the image by spreading the red, green, and blue tones evenly across the histogram.
To see the image histogram and adjust more advanced features like contrast, highlights, shadows, sharpness, de-noise, temperature, and tint, click 
.
You can open the Adjust Image controls in a separate window that you can move anywhere. Choose View > Show Adjust Image (from the View menu at the top of your screen).
To restore the image’s original settings, click Reset, or click Reset Image in the Adjust Image window.
Tip: You can also add these buttons to the toolbar: Adjust Image, Instant Alpha, and Mask.