Sometimes when I insert a photo at the top of a page I find I cannot manipulate it properly and discover that it is situated in the header, rather than on the regular page. I have to just remove the photo and insert it elsewhere. I don't understand how it gets into the header, since other times when I insert at the top of the page it works just fine.

That's almost certainly happening because you've clicked in the header/footer area before inserting the picture. You'll find it easier to see where your insertion point is if you click on the ¶ symbol on the Ribbon's Home tab to display formatting marks, including paragraph breaks and, if that's not enough, by going to File|Options|Advanced>Show document content, then activating the 'Show crop marks' option and/or the 'Show text boundaries' option.

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Cheers,
Paul Edstein
[Fmr MS MVP - Word]

It is really simple to enter the header by double-clicking in that area. I agree with Paul that showing the extra information will make the problem less likely.