One of the most fundamental questions in camera selection is what kind of signal it outputs. The main choice is between analog or digital, but there are also several different permutations within each of those categories. In general, analog cameras are lower cost, but generally have less noise immunity, flexibility in frame rate, and resolution. Unless you have a definite need for high speed, high precision, or operation in a noisy environment, an analog camera will usually be sufficient.
Analog cameras can output either a standard (RS-170, NTSC, CCIR, PAL, and so on) or non-standard signal. Standard cameras are easier to configure, while non-standard cameras provide different characteristics, such as higher resolution or frame rates. If using a non-standard camera, you need to make sure that the frame grabber you choose is configurable to support such a camera.
Digital cameras have some additional choices in the type of signal. Typical data transfer signal types include TTL, RS-422, and Low-Voltage Differential Signal (LVDS, or RS-644). TTL signals are fairly susceptible to attenuation and noise, and often can only be used with extremely short cable runs (a few feet or less in some cases). RS-422 and LVDS are differential signals which are much more robust, with LVDS allowing longer cable runs at lower signal voltages.
Anatomy of a Video Signal