Raster is sometimes known as Bitmap. Raster files are best for photos because they reproduce colour accurately.They are made from pixels, with each pixel coloured separately. This means that when you try to enlarge the image it becomes pixelated, meaning that the individual pixels are visible resulting in poor image quality.
Vector image files are made up of mathematical coordinates. The file sizes are smaller because only data is stored, and not individual colouring. Unlike bitmaps these images can be scaled up and down as much as you like and they will never lose image quality.
Pixel is short for picture element. Pixels are what make up a bitmap image file. They can create highly detailed pictures but aren't very good for resizing. Each pixel stores information on what colour it is and the size of it. Images made from pixels usually take up lots of space.
Resolution is the size of the picture. It also controls how much detail the image holds. Resolution is measured in DPI (dots per inch) this means how many dots are in a inch of the picture. High resolution images are highly detailed but take a long time to make. Low quality images usually have 72-100 DPI and are mainly used on the internet, high quality images have about 300 DPI but only when printed.
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