This includes both in text or in image form.
This has been stated many times.
As before, the mod team isn't ready to make it against the rules for OP's to post links in plain text because some people just want to give their games away without much hassle, but:
Please consider avoiding giving out game keys in plain text on the subreddit.
Please consider making people work, even if just a little bit for their prize. While the mod team isn't a fan of the random number draw, it sure beats dumping game keys in plain text. Consider other fun ways like "tell me a joke" or "link me to your favorite under 30 seconds youtube video". Also, remember that while the mod team is really harsh with users who use multiple accounts (and other forms of giveaway fraud) on giveaways, you as OP are still free to impose sensible rules that the winners must follow (like, "x month old accounts only, please", for instance, or "user must participate on the community, not just on giveaway threads").
If you just post keys in plain text, everyone with an internet access can have them. This is why people aren't thanking you. You have no way to make sure whoever got it even has a Reddit account to begin with. You also can not make sure people who we banned for giveaway frauds aren't getting those keys, because that way they still have the same chance as anyone else.
Perhaps you just want to dump keys for someone else, no matter who, to get them. If so, that is fine. We will not force you to give them away in any specific matter, it's just that you may prefer to give them out to fellow members of the community, and just posting keys in plain text or in images gives pretty much everyone on earth with a decent internet connection the same chance of winning.
Remember, PCMR has millions of hits each month and according to official Reddit data, only a fraction of the people who visit Reddit actually have an account. If you want to give away games to your brothers, make sure you are. Posting keys in plain text, even if on images, isn't how. If you don't care about that, then that's fine too.