I'm with Alexander on this one, I think that pre-puberty we could be either or but if we've had our issues with gender from a young age we just often appear awkward in female clothing when we look at old pictures.
Looking at me as a kid, I only smile when I'm in more gender neutral or boyish clothing. I don't think I was a particularly down kid, I remember having a lot of fun, but when I was in girlier clothes I think it was like I could just ignore it myself and have fun despite it, but when the camera came out, the camera couldn't ignore the clothes and I just didn't want the picture taken. I guess it's hard to explain. Needless to say, being as I went to school in Scotland where pretty much every school had uniforms, I look unhappy in almost every school photo because of the skirt. I didn't love school, but I did eventually make a few friends in high school and even pics with them I don't look too happy but only in shots where you could see the bottom half. Reason? Well I LOVED the school uniform from waist up. I insisted on unisex/guys shirts and so I'd wear a shirt with a tie, maybe a guy's jumper (in colder months) and then a blazer. It was like a suit...if you ignored the pleated skirt I had to wear. I never really acknowledged it at the time but photos of me waist up with friends in school when I had short hair, I'm happy. In pictures taken from further away where you could see my skirt, I look awkward, like I don't want to be there, and most often not smiling. Took me a while to think about it but it was purely an unconscious thing at the time and I can only guess that it's because the camera can't ignore what I forced myself to pretend wasn't there. Or to be more honest, I used to think of my skirt as being like a kilt. Hey, I'm Scottish after all and I can't wait to transition to a point where I'm comfortable enough to go out and buy (yes buy, not rent) a kilt!
It's also worth noting that in these pre-T photos, there's a very high probability of pics of them in female clothes when maybe they didn't know someone was taking a photo where they do actually appear happy or more "right" with their gender. But because they're showing off their masculinity, they might be hesitant to include any photos of them looking happy when feminine. If anything to stop all the haters ready to pounce with "You're not transgender - you looked happy as a woman!"
The thing is you don't have to be depressed and suicidal about being transgender, but outside the community (and unfortunately at times even within the community) there's this idea that unless you're extremely depressed to suicidal levels over it; it's not real. I've personally never been depressed or suicidal myself, more though the confidence to not care what others (unless it's my family) think. But even I would never put together a vid of before and after with any picture that anyone managed to get of me happy in female clothes, and I know there's gotta be a couple of photos out there like that because I've always been a bit of a joker within groups of friends. If I was putting together a vid I'd always chose an awkward photo to help almost justify it to haters, like, "Yeah, this IS right for me because look - I wasn't happy!" I don't need to justify anything to myself but would rather highlight the change with stark contrast, so I'd put in pics of me unhappy as a female and pics of me standing taller and being happy as a man. I guess that even if we didn't think about it logically like that, it's something we'd do subconsciously anyway because we're proud of the transformation and trying to show that off.