Social media and misappropriating photos ...

Seems harmless, take photo from a facebook account that isn't yours and use it on your own social media chat site or social media, right ?
Well … no.

I know, really obviously answer to that question.  It's wrong on so many levels.

Two points about social media and your perceived 'identity' …

Firstly, if you are using your own photos on your own social media.  The question of when is it misrepresentation crops up from time to time.  Lets face it, EVERY photo you see on Target, Wal-Mart, Kohls, JCPenny etc etc, are digitally modified in some way.  The reason being is that the photo is a presentation.  I hear so many guys comment on a girls 'boobs' on photo x, y, z on some bikini model and you have to roll your eyes as those 'boobs' aren't often real perse, they are digitally edited to look like softballs.  It's not the only tinkering that happens, but the biggest, 'down there' is another place, skin blemishes are another major one.
The point being, nearly every girl out there will tweak photos to fix eye glare, lipstick, pimples, wrinkles, the list is endless.  The same goes for professional portrait photography, it's a given that you will sit down with a photographer, get pictures taken and then a few hours in professional grade editing software.  It all comes down to photo composition.  
Now, when it becomes a problem is when maybe that original photo of you is so far removed from reality that it's more photoshop vs first gen photo.  Then it's up to the 'owner' to decide whether they publish it or not and if they do, how are they going to address comments to it ?  Implying that some angelic fairly tale rendition of you is the real you is misleading and taking credit more for the photo editing software vs actually 'you'.

Second, using other peoples photos.  Now, if you do this because you like the photo, I sometimes do, however … I comment on the photo who/what it is so that people can see that I am using a photo that isn't me and I am not taking credit for it and thus not being misleading in using it.

Before I get too deep in to why on the second point, you'd use someone else's photo as your own, well, identity theft, pretending you are someone you aren't for numerous reasons, baiting someone to confide in you to obtain personal information or more photos of a personal nature … endless.

So, given that a person is misusing someone else's photo from lets say facebook, instragram etc and they aren't using it for nefarious purposes, is there any harm in it at it's lowest common denominator ?
Actually yes.  I will give a simple example.  I have had photos taken off of social media.  Some of those photos are to me at least 'costly' relatively speaking.  If I have spent maybe 2-3 hours modeling which required me to lay on a cold hardwood floor and then have the photo run through professional digital editing software to get a composition, again hours, oh, also the equipment setup, backdrops, light boxes etc which takes maybe an hour, an extra person maybe.  My out of pocket cost on a simple looking professional composition maybe upwards of $600.  So, if you go to someone's facebook page who is a model whether professional or semi-professional and take a photo, you maybe taking many hours of work and additional hours of money from that person.
It's simple theft.
Ok, well, that's maybe a professional shoot, what about a selfie ?  Well again, if I have gone out and bought some clothes, decided I will share a photo of those clothes, what is the cost ?  Clothes, my time trying to take countless selfies, then because a mirror or your phone has anomalies, you have to fix the photo or it'll look like crap, so either way, you are spending an hour or two taking a selfie, unless of course you take that one photo and it just upload it and call it quits.  I don't, I try and not look like crap.  So, safe to say, most girl's selfies monetarily cost two hours of time, maybe then $50-$100 for a simple selfie.  Something to think about the next time you use your phone's camera.

There you have it.  The basic concept of 'borrowing' someone else's photo(s) is fundamentally theft of intellectual and artistic property.