This question is as broad as they come. The only question I have heard in philosophy which is potentially broader than this is, "What is the meaning of life?" and even then its highly likely that the two answers are intimately related. This question is certainly far too broad for Philosophy.SE, but I think I can speak to the broadness in an answer and provide more value to the forum than a mere vote to close, so I will do that.
What could determine the value of a person in a similar way to how I imagine ... their ethical behaviour does?
This sentence is quite tricky to work with, tying concepts of value and ethics together. I wanted to start off with some grounding, so it seems reasonable to quote the second paragraph from Wikipedia's article on Ethics:
As a branch of philosophy, ethics investigates the questions "What is the best way for people to live?" and "What actions are right or wrong in particular circumstances?" In practice, ethics seeks to resolve questions of human morality, by defining concepts such as good and evil, right and wrong, virtue and vice, justice and crime. As a field of intellectual enquiry, moral philosophy also is related to the fields of moral psychology, descriptive ethics, and value theory.
So right away we can see why this question is so difficult to answer. Ethics is concerned with the concepts of right and wrong, two cultural universals. Anyone who has stepped outside their own philosophical comfort zone is aware that there is great disagreement about right and wrong. There's so much disagreement that we will often go to war and kill each other over such disagreements, despite the fact that many of these peoples going to war have a moral code against killing one another!
Now consider the concept of value. By your phrasing which uses the term "a person" and the sentence "I mean something like their human worth." you are clearly talking about someone else, so this is not a question of self-value (which is good, because that is a far far harder concept). A value of another being would certainly be used to make decisions whether one should act or not. This leaves the question of whether the value of a human being is above that of all else, making human life sacrosanct, or whether it is something on the level of other things which can be traded. The former opinion is popular, but famous thought experiments such as the Trolley Problem or any of its many variants make those positions very difficult. In these experiments, we see just how much trouble we get in if we cannot include life in a series of balances.
The next question is whether this value is a one dimensional thing. Are we assigning a dollar value, or is this more like sports stats, showing varying facets of the individual? The latter often makes more sense, but makes for hard decisions if it comes down to trading that individual for someone else.
Finally, we can come down to what we want to go into that value in the first place. In the comments, Jobermark recommended exploring value according to the Greek tenses: 'doing' 'being' and 'being done to.' We can do this, but such an approach is not very universal. Many Asian martial arts seek a balance between 'doing' and 'being' which is ill captured by either word. There's also a strange region between 'being' and 'being done to.' Jobermark points out that there are few who value 'being done to,' but consider the value we put on the strong individual who chooses to just sit there and let someone beat on them until that person calms down rather than responding with actions. What about the man or woman with demons they hold back day by day, is there no value in that?
In the end, the only reason this question is answerable is because of the section of the first sentence which I omitted when I quoted it the first time. Here it is again, with my own emphasis on the removed part and its surroundings:
What could determine the value of a person in a similar way to how I imagine (because of a vaguely Christian upbringing I guess) their ethical behaviour does?
The only thing which can determine that value is you, but you may be able to hedge your bet by looking the valuations of Christianity in its most general sense.