The quality of an image's resolution is most often measured in pixels or megapixels. Pixels are tiny spots of color that, when combined with other pixels, make up an image. More pixels in an image mean a larger, more detailed image. A low-resolution image is typically below 640x480, with the first number indicating the number of vertical pixel columns and the second being the number of horizontal pixel columns. Multiplying these two numbers gives you the total number of pixels in the image. So a high-resolution picture with a resolution of 2,000x2,000 has 4 million total pixels, making it a 4 megapixel image, with a megapixel indicating a million pixels.
Before the advent of high-definition media like HD DVD and Blu-ray, many home video formats offered low-resolution quality (particularly in comparison with today). For example, analog VHS, which was the standard in the 1980s and '90s, was capable of a maximum resolution of only 330x480 lines. Laserdisc and Hi8 formats offered higher resolution than VHS at 560x480 lines, but they still paled in comparison with some of today's digital systems.
Much of today's digital media stores images at high resolution. DVD and Digital 8 formats are the lowest resolution digital mediums, but at 720x480 lines they are still higher than previous analog mediums. More recent high-definition media, like HDV and Blu-ray, are capable of storing images and video at resolutions of up to 1,920x1,080 lines.
The newest digital cameras are capable of capturing extremely high resolution images. Hassellbad, for instance, has a series of still cameras that can capture images upward of 39 megapixels, or 39 million pixels. In regards to video imaging, 4K cinema has become a recent trend, with cameras from companies like RED capable of capturing digital video at resolutions of 4,096x2,160 lines.
IMAX cameras capture the highest resolution motion picture images. These enormous cameras, which use 70mm film, capture moving images at around 10,000x7,000 lines that are played on screens upward of 90 feet high.