I'll correct you Cheyenne but Video card actually have Processor call VPU for Visual Processing Unit.

Here some info from Webopedia

Link : http://www.webopedia.com/TERM/v/video_adapter.html

Modern video adapters contain memory, so that the computer's RAM is not used for storing displays. In addition, most adapters have their own graphics coprocessor for performing graphics calculations. These adapters are often called graphics accelerators.
Graphics Coprocessor : A microprocessor specially designed for handling graphics computations. Most graphics accelerators include a graphics coprocessor.

Graphics Accelerator :
A type of video adapter that contains its own processor to boost performance levels. These processors are specialized for computing graphical transformations, so they achieve better results than the general-purpose CPU used by the computer. In addition, they free up the computer's CPU to execute other commands while the graphics accelerator is handling graphics computations.
The popularity of graphical applications, and especially multimedia applications, has made graphics accelerators not only a common enhancement, but a necessity. Most computer manufacturers now bundle a graphics accelerator with their mid-range and high-end systems.

Aside from the graphics processor used, the other characteristics that differentiate graphics accelerators are:

memory : Graphics accelerators have their own memory, which is reserved for storing graphical representations. The amount of memory determines how much resolution and how many colors can be displayed. Some accelerators use conventional DRAM, but others use a special type of video RAM (VRAM), which enables both the video circuitry and the processor to simultaneously access the memory.
bus : Each graphics accelerator is designed for a particular type of video bus. As of 1995, most are designed for the PCI bus.
register width: The wider the register, the more data the processor can manipulate with each instruction. 64-bit accelerators are already becoming common, and we can expect 128-bit accelerators in the near future.
I think that will help you understand deep inside how video card work.