YouTube Thumbnails

This could be due to making ingame screenshots and edit the background out till only the gun itself is left for example.
Other options people use is wallpapers wich they edit with txt and the usage of their own mark and such.

 

Yeah, its basically what Twilight said, but I'd also add for example BF4 you can preview the guns and stuff, so people take screenshots of that and photoshop it.

 

you can use backgrounds for the internet or just print screen while you are recording to make a decent thumbnail most of the time

 

Google search is my best friend for stuff to use in thumbnails.

 

For me personally, I get my Battlefield pictures from 3 sources:
1) Google search
2) Anatoli Pavlov (a guy that makes amazing Battlefield pictures)
3) Or I make them myself, using the Battlefield cinematic tool

 

Study some basic "GFX"
It can be useful for the basics...

 

I think with a Google you should find the images you need (make sure they're transparent png files and copyright-free); I used to use Inkscape to make the thumbnails after that.