Update: If you Galaxy S II is already upgraded to Ice Cream Sandwich Android 4.0.3 ( or other version of 4.0), to do screen shot: Press at the same time the Volume Down button and Power button for about 2-3 seconds.
What we mean here by using Home and Power keys combination on making screenshot in Samsung Galaxy S II GT I9100 is that there is a built in screenshot application feature on this SGS2 without additional trick or applications needed. Just using the combination of Home key and Power Key, you would able to capture the screen display on your Galaxy S2 and automatically stored and saved onto SGS2’s gallery images. Although there is also available for software to do screenshot on the Android Market (Google Play).
Here are the tutorial and instructional steps that you had to follow:
Note to success: Make it the 4 steps being done less than A SECOND
Use your both hand to handle the Samsung Galaxy S2 body. Forefinger of your left hand ready to press the POWER / LOCK button, and thumb finger of your Right Hand ready to push and hold the HOME BUTTON.
Second Step: Use your Thumb (Right hand) to PRESS and HOLD the HOME BUTTON.
Third Step: While HOME button hold up, PRESS the POWER Key with your Forefinger or middle finger (Left hand), and immediately release it!
Fourth Step: Release the POWER button. Done. You should make it all the steps under 1 second to make it 100% succeeded of screenshot action.
And for the example result you can see at the images below
This trick would also works on other version of Samsung Galaxy S2, such as on SGS2 SGH-i777 for ATT, SGS2 SGH T989 for T-Mobile, SGS2 SPH D710 for Sprint (Galaxy S2 Epic 4G Touch), and even SGS2 SGH i727 Skyrocket 4G for AT&T.
Remember: PRACTICE MAKE IT PERFECT!
PS: The image captured and edited using Samsung Galaxy Note with its S-Pen