Showing a bit of flesh, or all your flesh for that matter, isn't objectification. Objectification is rooted in what's being communicated, so its much more dependent on the subject and publication's reasons and context.

Trite examples: Picture of Bikini Clad girl visualizing results of weight loss through hard work, healthy eating, and going to gym for purposes of promoting a better lifestyle = not objectifying

Picture of Bikini Clad girl indicating you need to buy XYZ or you'll never be beautiful like this specimen = objectifying.