Can I use images showing up in Google search for my presentation slides without violating any copyright?
You can use images showing up in Google Search if and only if the license allows for it.  Therefore, you might be interested in Advanced Google Image Search, where you can search by copyright status. More information about the Usage rights search can be found here.

For example, here are freely useable images searching for "Mars".  Notice how many of them are from NASA or the Wikimedia Foundation.

And here is an example searching for "IBM".

Note: See the important remark by @jb. in the comment below
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 you should verify with the original source (1) that the picture really is free to use, and (2) under what conditions

Good luck and enjoy!