Web-accessible cameras involve a digital camera that uploads images to a web server, either continuously or at regular intervals. This may be achieved by a camera attached to a PC, or by dedicated hardware. Videoconferencing cameras typically take the form of a small camera connected directly to a PC. Analog cameras are also sometimes used (often of the sort used for closed-circuit television), connected to a video capture card and then directly or indirectly to the internet.
The oldest webcam, as the technology came to be known, still operating is FogCam at San Francisco State University, which has been running continuously since 1994.
As with many new technologies, webcams and webcam chat found early commercial adoption and aggressive technology advancement through use by the pornography industry. The adult industry required 'live' images and requested a Dutch developer to write a piece of software that could do this without requiring web browser plugins. This led to the birth of the 'live streaming webcam', which is still available in various forms today. and is still being updated and upgraded.
One of the most widely reported-on webcam sites was JenniCam, started in 1996, which allowed Internet users to constantly observe the life of its namesake, somewhat like reality TV series Big Brother, launched three years later. More recently, the website Justin.tv has shown a continuous video and audio stream from a mobile camera mounted on the head of the site's star.
Recently, Apple and other computer hardware manufactures began building webcams directly into laptop and desktop screens. This eliminates the need to use an external usb or firewire webcam.
In addition to use for personal videoconferencing, it was quickly realised that World Wide Web users enjoyed viewing images from cameras set up by others elsewhere in the world. While the term "webcam" refers to the technology generally, the first part of the term ("web-") is often replaced with a word describing what can be viewed with the camera, such as a netcam or streetcam. Educators can use webcams to take their students on virtual field trips.
Today there are millions of webcams that provide views into homes, offices and other buildings as well as providing panoramic views of cities (Metrocams) and the countryside. Webcams are used to monitor traffic with TraffiCams, the weather with WeatherCams and even volcanoes with VolcanoCams. Webcam aggregators allow viewers to search for specific webcams based on geography or other criteria.
The captured files can be saved locally, uploaded to an internet server (via  or ) (from which they can be made accessible to anyone over the web), or privately e-mailed to the user per predefined rules. Options for image size and quality, overlaying logos, and time stamping images are usually available. File names can be sequential numbers or current time. Some software allow automatic erasure of old files when not needed.
Some software can remotely control certain brands of cameras, allowing rotation and tilting.
As webcam capabilities have been added to instant messaging text chat services such as AOL Instant Messenger, one-to-one live video communication over the internet has now reached millions of mainstream PC users worldwide. Increased video quality has helped webcams encroach on traditional video conferencing systems. New features such as lighting, real-time enhancements (retouching, wrinkle smoothing and vertical stretch) can make users more comfortable, further increasing popularity. Features and performance vary between programs.
Videoconferencing support is included in programs including Yahoo Messenger, AOL Instant Messenger (AIM), Windows Live Messenger, Skype, iChat, Paltalk (now PaltalkScene), Ekiga , Stickam, and Camfrog.
Some online video broadcasting sites have taken advantage of this technology to create internet television programs centered around two (or more) people "diavlogging" with each other from two different places. Among others, BloggingHeads.tv uses this technology to set up conversations between prominent journalists, scientists, bloggers, and philosophers.
FreeTrack is a free webcam motion tracking application for Microsoft Windows that can track a special head mounted model in up to six degrees of freedom and output data to mouse, keyboard, joystick and FreeTrack supported games.
The EyeToy for the PlayStation 2 (The updated PlayStation 3 equivalent is the PlayStation Eye) and similarly the Xbox Live Vision Camera for the Xbox 360 and Xbox Live are color digital cameras that have been used as control input devices by some games.
Small webcam-based PC games are available as either standalone executables or inside web browser windows using Adobe Flash.
Webcams typically include a lens, an image sensor, and some support electronics. Various lenses are available, the most common being a plastic lens that can be screwed in and out to set the camera's focus. Fixed focus lenses, which have no provision for adjustment, are also available. Image sensors can be CMOS or CCD, the former being dominant for low-cost cameras, but CCD cameras do not necessarily outperform CMOS-based cameras in the low cost price range. Consumer webcams usually offer a resolution in the VGA region, at a rate of around 15 frames per second. Higher resolutions, as well as higher frame rates of up to 30 fps, are also available from the brands like Microsoft, Logitech, and HP.
Support electronics are present to read the image from the sensor and transmit it to the host computer. The camera pictured to the right, for example, uses a Sonix SN9C101 to transmit its image over USB. Some cameras - such as mobile phone cameras - use a CMOS sensor with supporting electronics "on die", i.e. the sensor and the support electronics are built on a single silicon chip to save space and manufacturing costs.
Most webcams feature built in microphones to make video conferencing more convenient. Creative Technology has introduced a webcam featuring built in noise cancellation to focus the audio to the speaker who is directly in front of the camera, excluding ambient noise.
The USB video device class (UVC) specification allows for interconnectivity of webcams to computers even without proprietary drivers installed. Microsoft Windows Vista, Linux and Mac OS X 10.4 & 10.5 have UVC drivers built in and do not require extra drivers, although they are often installed in order to add additional features.
In mid-January 2005 some search engine queries were published in an on-line forum which allow anyone to find thousands of Panasonic- and Axis-made high-end web cameras accessible through the web. Many such cameras are running on default configuration, which does not require any password login or IP address verification, making them visible to anyone.