As far as I know you can't; you have to use the crew emblem creator tool in the social club page.
how do you import picture / pictures to be used as your crew emblem?
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You can with a little browser-trick. It doesn't hurt anything and it's not glitching/cheating.
You can find some tuts at Google. Search for: 'Social club emblem image'. I'm sure you will find it.
they patched it