@Background Pony #0357  
Like @Nightweaver20xx said, it’s fairly random. Sometimes (easter, april’s fools day, karpet-shark) a pic is featured because it’s relevant to the time of the year; other times it’s an old classic.
 
Another factor that (at least for me) plays into account is how many votes a pic, and artist tag as a whole, has (at the time of featuring, that is). Although there are always exceptions, etc.
 
Overall, for this one the previous one was just way overdue for a replacement, this one was nice (haven’t seen this art style around a lot), didn’t have a crapton of votes already, so why not?
 
@Nightweaver20xx  
Now hang on, we do actually have a Featured Image suggestions thread, from which things actually do get picked from time to time. Not all of them though, and I generally tend to ignore the ones having a score of 150 or higher altogether. That, and animated pictures.  
We don’t really plan ahead or anything. Usually one of us goes “uh, we probably need to set a new featured image” and then we just open some pictures and choose one.

@Background Pony #0357  
Because featured images are up to the decisions and personal tastes of the site runners, not us.

I don’t have anything against the artist but… why is this featured? I’ve seen waaaay better drawings.

Am I the only one who thinks this looks like something out of Transformers Cybertron?  
 
Change the images around a bit and you’ve got something…

@pokemonFTW u

@Comisdazied  
Well isn’t that a nice backhanded comment.

@Background Pony #BEAA  
Hey, it’s still better than another one of karpet-shark’s images being featured.
 
But that’s not really saying much.

Friendship is also available to dragons.

If you happen to see any of these ponies, arrest them immediately.
 
The crime, you ask? They’re thieves. They stole my heart.

@HunterSClopson  
It is more of an eyesore. I don’t hate it, but it is much closer to sucking than to being great.

The usual suspects.

Now that is pure eye-candy.

@pokemonFTW  
This is the truth.

The coloring is so lazy, that its artistic