Mind you I think your definition needs a bit more formation since hardly ANY female character is purely objectified.
But objectification can take place
within characterisation.
If you have a female character who is helpless, or who is adored by the male protagonist and this adoration then drives the plot, or who is "saved" in the end by the protagonist, then the characterisation of that female character only exists to pander to male fantasies of being strong, masculine, saving the day, being in control and, ultimately, having the woman to himself and therefore controlling her.
It should also be borne in mind that, while women are objectified in the real world as well (eg. showgirls, the behaviour of teens in school, sexual offenses in the workplace), this is no excuse for objectifying women in film/books/games. The reason the real world objectifies women is because the real world is, for the most part, a patriarchal sphere in which women are seen as either prizes to be captured or hopelessly inept people who should leave anything complicated to men.
(This has got a lot better over the past century or so, but given the way women are sometimes treated in the workplace - via groping or the expectation they'll sleep with the boss - or on gaming forums or within tech culture - "Sorry, you're a woman so you can't possibly understand technology - can I speak to a man please?" - it's clearly still with us in some sense.)
Now granted, an accurate representation of the real world and its patriarchal bias will result in an artwork which recreates these situations. The key, though, is to present them but not to endorse or practice them. If a woman is presented sexually in a videogame and objectified by other characters, a valid response from the game would be to present the woman as a complete character and show what effect this sexualisation has on her - perhaps she feels uncomfortable being looked at all the time, for example. (A good example of this is
Silence of the Lambs, which showed how uncomfortable Clarisse was as a female police officer, ie. in a man's world.) What the game should not do is just roll with the sexualisation and have the woman accept it
to the extent that it eclipses the rest of her character. Sexual women are fine: people are sexual. But making a character sexual to the point where she exists largely to fulfil the fantasies of male players means that she herself, as a character, is simply an object. Yes all characters are fictional anyway and are to some extent objects, but the key is to give the illusion of depth, to suggest that there might be more to a woman than large breasts and a tendency to need to be rescued.
