Meaning:

A pixel, short for "picture element", is the unit of measurement for the size and quality of a digital image or display.

An image size of 1280 x 720 pixels is large enough to be HD standard and is commonly used in photography and film. This size uses a 16:9 aspect ratio, which is also common in filmmaking.

How does pixels look like?

If you enlarge an image you can see that it's getting blurry and has like squares in it. (see picture)

The less pixels it has the more blurry it will get so be sure to take one that is high numbered.
Example a 1280 x 720 is higher then a 400:300

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