These types of graphics are resolution independent so no matter the size, they'll display with the best resolution available to the viewer
A raster/bitmap graphic has three dimensions: width, height, depth
The smaller the depth, the bigger the size of the image.
The more colors in an image the richer the pixel depth
In a photograph, a higher depth is more desirable because it producer a richer image quality
When using a simple logo, a richer depth is desirable because it creates a smaller filesize
When displayed on a monitor, television or printed vector graphics are always converted into bitmaps and output at the highest resolution of the device being used.
The oldest of the modern graphic formats which supports 256 colors
The format that supports animation
This format supports 1-bit transparency, but with limited color information
When importing an image from a digital camera, it's important to crop the images but it isn't important to re-save them to make them smaller
When compressing images, it's a good idea to understand the target sizes of your devices and resize accordingly.