Stated nicely by Paul Anderson...
There will be occasions when you want to capture what's on your computer screen and put it in an image file. Unless the entire screen contains only a very few colors, try to take the screenshot on a computer with a high-color or true-color display. This is especially applicable when you're capturing a Web browser [or TSO!], as browsers frequently dither or substitute colors when running on an 8-bit display. If you have no choice but to grab a screen in 256 colors, at least turn off dithering.

In Windows, you have two options. Press the Print Screen (or PrtScn) key on your keyboard to copy the entire screen to the clipboard. Press Alt-Print Screen to copy only the active window.

You have more choices on a Macintosh. Pressing Command-Shift-3 creates a PICT file of the entire screen in the top directory of your boot drive. Press Command-Shift-4 to change the cursor to a cross, which you can click and drag to select an area of the screen to capture in a PICT file. The same combination with Caps Lock activated changes the cursor to a circle; click a window with the circle to create a PICT of that window. Adding the Control key to any of these combinations copies the screen image to the clipboard.

For X Window desktops such as GNOME and KDE, the command xwd -out filename.xwd lets you click a window to make an XWD image of it. Adding the -frame option will capture the entire window manager. The popular utility xv also does screen captures, and KDE comes with the utility ksnapshot.

Step 2 - What to capture

It's important to always note the following in a trade with someone:

Show us the entire conversation - what you or the seller compromised on before being scammed. (IMs AND room chat)

Collecting person's name if going to another city (and verifying before doing the trade).

Showing store messages on what the person baught is useful.  To be more clear, please click the following slideshow to see how I do safe transactions.  (I make these files in case someone says I scammed them.)  Every picture is needed at the end - to show I return everything.  *You can use this tip vice versa to show if you don't receive all items.
Slides 1 + 2 are most important.  Notice how I take the screenshot quickly as the message "Transaction Succesful!" appears.  Without this - you have nothing.

You want to create many pictures, appearing as though a film, to properly catch a scammer.
(keep saving document!)

Step 3 - Saving your picture

Open any word processing program of the following:

Microsoft Word

AppleWorks

WordPerfect
All you have to do is go under Edit and click Paste.  If you copy something else (such as text) between the time you took a screen shot and are about to hit paste, you're not going to be able to paste the picture.  The computer can only copy one thing at a time.  Save your work often.

Step 4 - Alert the community!

Send all screenshots to me, Lonely Stranger, at TSO_LS_Central@yahoo.com.  Upon looking over your work, I will decide whether the sim should be under Proven Scammers or Potential Scammers at TSOrevolution.  It helps to add your sim name and city too.

Even if you were scammed and didn't get screenshots - send me some names of other victims to help convince me they should be under Potential Scammers.

Important reminders

You can only screenshot 1 picture at a time.  You must keep hitting Print Screen, then paste, Print Screen, then paste.

The form of taking a computer picture of your screen is refered to as "SS" (snap shot / screen shot) or "PS" (print screen - the name of the button on the keyboard).

E-mail me to clear up anything else, Good Luck,

~LS