That's not really how copyright works. What you have now is an image with several rightsholders, each of whom has a copyright interest in the work. The rightsholder(s) in the Apache2-licensed image still have an interest in the work you've made, as do you.
You don't, and can't, own the image. Anything you do with the image, you will need to do in accordance with the Apache2 licence under which you made your changes.
You do own your copyright interest in the image (assuming you didn't create it for someone else, and that it doesn't fall under the local equivalent of a work for hire doctrine, if any). You may benefit from, license, or otherwise dispose of, that interest as you please. In countries with a doctrine of copyright that recognises authors' moral rights as well as economic rights, note that the moral rights are often inalienable (ie, you cannot dispose of those).
Nobody can meaningfully steal that image from you. It is possible that somebody might use copies of the image in a way that infringes upon your copyright interest in it; that will depend on the terms (if any) under which you made the image available to others. If somebody does that, you get to sue them for copyright infringement, if you want.
If you will forgive me, misunderstandings like these often arise from thinking that the law treats intellectual property just like it treats physical property. But law doesn't do that, generally. In my opinion, it's worth reading Richard Stallman's arguments against the use of the term intellectual property. I don't necessarily agree with everything he says there, but it's a useful counterpoint to the common MPAA/RIAA-driven view that copyrights are property rights, and that copyright infringement is morally and legally equivalent to theft.