(edited 11-12-2017 after comments below)
MS Windows User Experience Interaction Guidelines suggests the following:
“Use the second person (you, your) to tell users what to do.” So use second person for error messages, help, window or page labels, on-page documentation, and other places where the app is telling the user about the user’s content.
“Use the first person (I, me, my) to let users tell the program what to do.” So use first person for buttons, menu items, and other controls where the user commands the app.
This means you can have first and second person on the same page. You can label a list “Your photos” but have a button labeled “Publish my photos.”
This is consistent with what a user learns in the physical world, where the reader of text is “listening” to what the creator or owner of the text has to say, so the reader is “you” (e.g.., “We appreciate your business” on an invoice, “Your speed” on a radar speed sign, and, of course, any instruction, like “RSVP”). However, there is an exception for text artifacts that are handled by the reader as a form of communication back to the creator/owner (e.g., a contract, waiver or oath will begin “I, [PRINT NAME], agree that…”). That is like a command button label.
All that said, the correct answer to your question may be to not use either “My” or “Your.” Unless you need to differentiate between content under user control and some other content (e.g., community documents or photos), the best title is simply the class of content (e.g., “Documents” and “Photos”). Labels should start with the most distinguishing and informative words so users can easily scan for them. Cluttering your labels with low-meaning words like “my” and “your,” (or “view” or “manage”) makes it harder for the user.
Even when you do need to differentiate user content from others, you may want to avoid “my” and “your” because in certain situations it can be unclear if it refers to the user or the computer/ program/ website, or creator thereof. Links can be problematic. Consider a website for someone who writes and posts Game of Thrones fanfic, and invites her readers to post their own too. There’s a link for “My Stories” and “Your Stories.” Which is for the user and which is for the website owner? I believe some users will read the “Your Stories” link as “click here for your stories,” so they expect the users’ stories. Other users will read “Your Stories” as “show me your stories,” so they expect the website owner’s stories.
Or consider MS Window’s “My Documents” folder, which, at first, I’d say is direct violation of Microsoft’s own guidelines. But that assumes users perceive the folder to be a container labeled by Windows, so Windows should be “telling” the user it’s Your Documents, not My (Window’s?) Documents. However, some users may have a more interactive attitude and see the folder icon in the tree of Windows Explorer as a button that commands Windows to show the user's content, so it’s saying “(Open) My Documents.” If I buy and display an “I love my dog” bumper sticker, then it’s me talking about my dog, not the sticker-maker manufacturer talking about its dog. Likewise, some users may perceive they bought Windows (regardless of what the license says), it’s their workspace, so any labels therein are now them declaring their own respective ownership, so it should be My Documents. There’s a similar problem with social media web sites. Some users may perceive themselves posting on the web site’s page (so it’s “Your Posts”), while others perceive the web site “gave” them a page for their respective posts (so it’s “My Posts”).
If your program/ website doesn’t “own” any documents, photos, orders, or whatnot, maybe all users can figure it out whether you use My or Yours. Or maybe not –do all of them know there’s nothing there you own? You can avoid the risk of ambiguity by consistently using [Username’s] Documents, if it’s necessary to differentiate.