This images is linked via an absolute URL and is part of some other website. The alt attribute defines text that will display if the image cannot be loaded (try by adding a typo to the src attribute to see this in action, not all browsers handle this the same way). The title attribute defines text that will display when the user hovers the mouse over the image.
This images is linked via a relative URL and is part of this website.
You can size an image by setting its height and/or width in pixels. Hover over each image to see its dimensions. If you only set height or width then the browser will scale the other dimension automatically. If you set both dimensions (and not in proportion) then the image will appear squished or stretched.