If memory serves, the in-game screenshots that are saved to your screenshots folder in the CoH directory don't show the costume creator overlay. That is, however, usually captured by the Windows clipboard when you hit the PrintScreen key. You just need to paste it into something (MS Paint, Photoshop, GIMP... Facebook. I don't have an Instagram account, but you might be able to paste it there. Other image hosting websites might also let you paste from the clipboard.)