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Every image is comprised of a series of dots. The density of those dots is known as "resolution". You'll lean how to adjust image resolution in this video.
You will learn how to adjust the size of the canvas containing an image in Photoshop.
You will learn how to use the crop tool to resize images in Photoshop
A crooked image can be fixed. In this video, Mark will show you how to straighten a crooked image and then crop it in Photoshop.