Click the Crop
tool 
.
On the Tool Options palette, select an option from the Snap crop rectangle to group box:
Layer
Opaque 
Selects opaque areas of the current layer.
Merged
Opaque 
Selects opaque area of all layers.
Use this feature to eliminate transparent areas at image edges. The Crop tool can automatically set the crop area to cover just the opaque (non-transparent) area of a single layer or an entire image.
Note: Opaque areas that are not rectangular, may have transparent areas remaining after cropping.
To crop to the opaque area of a layer or image:
Click the Crop
tool .
On the Tool Options palette, select an option from the Snap crop rectangle to group box:
Layer
Opaque Selects opaque areas of the current layer.
Merged
Opaque Selects opaque area of all layers.
Note: If any layer or the background has a solid color (non-transparent) background, the entire layer or image is selected as the crop area.
Adjust the crop area as needed.
When you're ready to crop the
image, double click the image, or click Apply
in the Tool Options palette.