I want to make a facial recognition project but my coding ability is very limited so I am going to be relying on other peoples code but if i use their code even if i change the variables and make different functions to add their code under would that still be considered plagerism ?
You should clearly talk to your supervisor or advisor about this, however there are some general principles you are often overlooked by students when doing their final year projects in computing disciplines.
Firstly you should be clear what plagiarism really is and fully understand it. Plagiarism is presenting someone else's work as your own to gain credit for it as if you had created it yourself. However, we all use the work of others. We read books, we read tutorials on the Internet, we read things on Stack Exchange. We should, if doing this properly be citing the work of others properly so it is clear when ideas, code, formulas and other elements of our work are attributable to others. If we have properly attributed the work, then those who assess you can clearly see which parts are yours and which are not. Then no plagiarism is involved. A good student will be reading much and citing much and will be including the work of others. It is just they cite it well. A weak student may often be someone who has read little, used little, cites nothing and hands in little. A really bad student would just hand in someone else's stuff. Hopefully the boundaries are a little clearer.
The next element, particularly for Computer based projects, is to realise that we are using the work of others and including it in our project all the time. You will be using an operating system, you will be using a language invented by someone else a compiler built by someone else that interacts with run-time libraries that were supplied with it. Yet, despite doing this all the time students worry little about these elements that were included in their submitted project. Where is the dividing line between the bits that are incorporated in your work and what you did? Who can tell? This is why citing everything you used is important.
The only way to really make the whole project fully self-created, you would in extremis have to start with clean sand, make your own processor chips to your own design, write the operating system and compilers for them to your own design and then use that as a platform for your project. But, of course, that is totally preposterous.
As Isaac Newton is credited with saying, we can see so far because we are standing on the shoulders of giants. You should do the same. Select the best components and use your skill and education to assemble them into the best creation that is your project. All good things are just made from components that are acknowledged and this is not plagiarism. The skill is in using the right components assembled in the right way.
How many of those things should be hand-crafted by you and how many are imported is the guidance you get from your project supervisor.