It appears the Designer 'Terms of Use' also says it is essentially it is up to you to verify you are not copying someone else's work. You can do this by running your images through online image copy checking tools, as described in my previous post.
"Microsoft expressly disclaims any and all representations or warranties, express or implied, that any Creations (including Your generated Creations) do not infringe or otherwise violate the intellectual property rights of any third party.
Microsoft strongly recommends consulting legal counsel regarding any use You intend to make of the Creations.
You will indemnify, defend, and hold Microsoft harmless from and against any and all costs, expenses, and losses (including, without limitation, settlement costs and payments, attorneys’ fees, liabilities, claims, obligations, judgments, fines, and damages) incurred through claims, alleged claims, or threatened claims that Your generated Creations infringe or otherwise violate the intellectual property rights of any third party."