Questions about screenshots

anon1234 said:

I think an image might have a virus in it, I know that just by looking at it I may have gotten a virus

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Firstly, on what basis do you think an image has a virus "in it"?
There are no known viruses for OS X in the wild. Double clicking on an image file will not run any code contained inside it. It will simply display the image in Preview or other app. There is no known mechanism for a virus to propagate through an image.

If the file is actually an executable piece of code, pretending to be a picture, so that when double-clicked it will run, then you should notice that there is no image (unless it's a brilliant piece of stenography) when you QuickLook it. Also, if it the code wants to modify your system files in any way, it would require your admin user and password credentials, which you would have to type in.

anon1234 said:

can I take a screenshot using my mac instead of saving it?

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Yes: a screenshot is just an image file of the screen data, not of the original image file.
(Have you been watching too much Doctor Who?: An image of an angel becomes an angel itself!)

Macs are not immune to malware, but no true viruses exist in the wild that can run on Mac OS X, and there never have been any since it was released over 12 years ago. The only malware in the wild that can affect Mac OS X is a handful of trojans, which can be easily avoided by practicing safe computing (see below). 3rd party antivirus apps are not necessary to keep a Mac malware-free, as long as a user practices safe computing, as described in the following link.

Read the What security steps should I take? section of the Mac Virus/Malware FAQ for tips on practicing safe computing.