In light of this is, let me share three areas where I think we are particularly susceptible to falling into the sin of objectifying other human beings.
Lust, in effect, looks at another human as nothing more than the means of achieving one's own sexual pleasure. Apart from the very serious consequences of sexual sin to which lust might lead, treating a human as less than the image of God for the sake of personal gratification is the underlying, and by far, the more immediate danger. Unfortunately, we live in a lust-indulgent world and so must be discerning in guarding our hearts, and particularly so in regard to how we see other people.
If left to boil too long, anger has a way of transforming one we're angry with into a mere source of irritation (rather than a full-orbed person). As in the case for a pebble in one's shoe, it makes perfect sense to remove a source of irritation. We need to be careful, however, because anger imposes its own logic which rationalizes whatever retribution it drives one toward, regardless of how out of harmony it might be with the ways of God.
Envy has a way of seeing the envied as unworthy obstacles the envious would like to displace in the quest for self-satisfaction. Those seen as undeserving obstacles are also seen to lack virtues like perseverance, grace, creativity, etc. and so are perceived as getting a piece of the pie more fitting for the envious. So envy assaults God not once, but twice. It fails to see God's image in the envied, and it calls into question his wisdom in governance.
We cannot afford to allow lust, anger, and envy to shade our perceptions or color our treatment of other people. To do so brings us perilously close to that which Jesus condemns. If the one we count on to forgive us condemns us instead, where can deliverance be found? Before we act in thought or deed in regard to another human being we need to take a breath, especially when one of these three areas are involved, lest we fail to see the image of God and fall into sin.