In most cases the person taking the photograph will own the copyrights. The argument for joint authorship is valid assuming the person taking the picture (and the settings/etc) was almost entirely under your direction. And there are many reasons why this is very unlikely to come up as an issue in the first place (most know little/nothing about copyrights). But there is another legal consideration which I think is probably most valid/relevant... the **implied/verbal contract between you and the person who took the picture for you.
The picture was taken at your request, and handed back to you with no comment/limitations made. There are only two plausible reasons for this interaction.
- they know that you cannot do anything with the image, so they took it because it didn't matter... it's as good as if they did not take the picture at all. Or,
- they don't care about the copyright, at least in terms of your use of the image. It is understood that the purpose is as a keepsake of the moment and that you would most likely reproduce it (copy), show it to others (make public), and quite possibly edit it extensively (derivative work/copy)... that's three out of four.
Which seems more plausible? Which is a judge more likely to lean towards? If the person taking the image knows about copyright, and required no contract/limitations, that almost necessitates an implied contract for your use. And even if they did not know about copyright, the lack of concern/limits expressed also implies an understood agreement/implied contract.
The only right I think could still potentially be problematic is publication (sale/profit)... it is not illogical to assume a tourist asking for a keepsake image isn't likely to sell/use that image for profit. And even then there would be a lot of factors at play; how much (financial) harm/gain is involved, who is more culpable (should know the laws/unfair contract), etc.
And you probably don't want to claim authorship of such images. Just from a moral standpoint if nothing else (since you are aware of copyrights/moral rights).
**technically, because you did not exchange something of value it would not be a legal contract; it would be a gift.