As of May, 2017 (*updated), here are the most reliable instructions to take a screenshot of a running program on your computer, with the built-in tools of its system software.
Android devices except Samsung Galaxy devices: Hold the Power button and hold Volume Down for a moment. You must press both in at the same time, then hold both. The picture will go into your Pictures or Photos folder. (You’ll probably also get an “Alert” so you can share it easily.)
- Samsung Galaxy devices: see Lifehacker’s guide to taking screenshots on Samsung, and other Android devices.
Atari 2600: Why, you must be planning to play Skyline? You can hook up an actual Atari computer to a video capture device on your computer, but that could require some “tweaking” to get a capture, because the 1977 hardware doesn’t exactly follow all the rules for an NTSC TV signal.
If you download a ROM Image file of the game, you can use the Stella emulator to take a screenshot by pressing F12.
However, many Atari games (including Pac Man, and Skyline!) use “multi-field” drawing (aka “flickering”) to produce a display. To get a reasonably good screenshot, I recommend the following settings: (Press Tab for options, then click Video Settings) — General tab: TIA Zoom: Zoom 2× or higher; TIA Palette: Standard; TIA Inter: Nearest; NTSC Aspect: 90; ✓ VSync; ✓ PAL color-loss; TV Effects tab: TV Mode: S-Video; Scanline settings: Intensity: 25; ✓ Interpolation.
Commodore 64, 128, VIC-20, Plus/4, 16: on actual hardware, you’ll need a cartridge like the Super Snapshot or Action Replay to capture the screen image, either directly to a compatible printer, or save to disk, usually in Koala Paint or Doodle format. Many of these cartridges will not capture sprite graphics, like mouse pointers or game characters.
In 2017, however, you can use the VICE series of emulators and capture a screen image or video. From the Snapshot menu, near the bottom, choose Save Media File… and then choose to record a screenshot or screencast (video).
ChromeOS (ChromeBook, ChromeTop):
press Control + Shift + “switch windows” key.
The saved picture will be in your Downloads folder.
Fedora, Ubuntu (or most other Linux® systems): (Gnome Desktop)
You can take a screenshot (of one window) by holding Alt and pressing the Print Screen (or PrtScrn) key — they’ll be saved into your Pictures folder. To capture the whole screen, just hit Print Screen by itself.
Gnome also has a screen recording (screencast) function. Hold all of Ctrl+Shift+Alt and press R to start recording. A red “recording” icon will appear next to the personal menu, at the top-right area of the screen. Press the same keys again to stop. The video is saved in your Videos folder.
iPod Touch, iPhone, iPad: You can capture the screen on your iOS device using the Sleep/Wake and Home buttons. Press and hold the Sleep/Wake button on the top or side of your iPhone, iPad, or iPod touch, then immediately press and release the Home button. You can find the screenshot in your Photos app. Hold your finger on the photo for about a second to get the option to copy it, then paste it into an e-mail.
Linux other than Fedora: Usually, either Print Screen or Alt + Print Screen will work, but if not, look for a program named Screenshot in your applications overview or Software download area. On some systems, it may be called a “Screen Picture” instead.
macOS: Hit Command ⌘+Shift+4, and wait for your mouse pointer to change from an arrow to a “+.” Then, press Space bar, (your mouse pointer will now be a camera) and click on the window. The picture will go to your Desktop.
PlayStation 4: Hold the Share button for 1-2 seconds. You can only send this picture to your Facebook or Twitter feed. IGN’s guide has more details on PS4 screenshot sharing.
Wii U: Press the Home button on the bottom margin of the GamePad to share to Miiverse (using the Miiverse app) or Twitter, Tumblr, or Facebook (using the Web Browser app). Step-by-step instructions on Image Share from Nintendo.