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Yes, thats OK with proper credit/link.
@rpm give's us permission to use his logo, and I give the permission to use my creation.

But what is the best way for give proper credit?
(maybe:

or
'image created by @ctf with logo from @rmp' 'created by @ctf and @rpm' ).

I would do it like this:

A Steemit Flag)(image by @ctf and @rpm via:

as well as offer a tip or percentage of post payout

Oh, thats great :)

I will keep it on my list for future use.

see: Welcome to Art-Services for more examples of how I work with artists here on steemit <3