I came across a ridiculously old post that was designed to help with just this issue, I will post it beneath this comment. In the intro it said something and I began to remember some issues I had... The photo you choose must be hosted somewhere other than your device.

If I am talking rubbish I am certain a grown up or somebody capable will come along and correct the mis/dis info I am giving you haha. Check out this post though and see if it helps...

@msg768/steemit-help-how-to-change-your-profile-picture

If it doesn't help. Reach out and I will see if I have had a response from the people I submitted your query too that explains it better.