Pasting Images

Normally, you can simply paste an image into Confluence. If it does not work, it’s probably because of this:

When I copy an image that has clear space in it (grey and white checked background in Snagit) it doesn't copy the image properly so when I try to paste it in confluence nothing happens.

If I fill the clear space with white for example, then the image copies and pastes successfully into Confluence, therefore it's a Snagit / User error nothing to do with confluence.

Outlook

Often images copied from Outlook emails don’t paste into Confluence. Just paste them into a bitmap editor (Paint, Irfanview etc.), and copy from there; this will paste into Confluence.

Snag-It

I am using Snag-It, and have the same problem.  What I do is copy the image and paste it into mspaint, then copy it from there to paste in Confluence.  I would have never figured that out until I read your thread.  

I ran into a similar problem with SnagIt.
Workaround:  in snagit, right click on the image, select Canvas Color...
Choose a color and then save the image (Ctrl+S)

You can now copy+C/V the image into Confluence without any dramas.