Maddeway, I see this is your 3rd posting, so welcome to RP in case no one has said so yet.
Typically the photos you see here and mostly everywhere are Bit Mapped graphics. The images are basically made up of thousands or millions of pixels - single colored dots which in aggregate make up the image. If your image resolution is 300 dots or pixels per inch and you draw a 1 inch x 1 inch square and fill it with say blue, then that square will contain 90,000 blue dots which make up that square.
Vector graphics use a different approach. Instead of pixels, they use mathematical formulae to represent shapes and color fills. So i the case above, a vector graphics programs (like Illustrator, or Microsoft Powerpoint) would have a series of instructions to draw a square represented by 4 lines of a certain length. Vector graphics, being mathematically defined end up generating files which are very much smaller in size than bit mapped graphics. The graphics also tend to product much sharper lines without the jaggies you see in some shapes drawn in bit mapped images.