I have a bit of a dilemma. I am writing a master thesis about a topic that I originally thought was original. It turns out that someone else has done the exact same thing, which forced me to take another perspective on the same topic. Their code and research are old, over 10 years. What I ended up doing is migrating their code to the newest version of the framework used and then evaluating the method in a real-world environment.
Now I am in a situation where I have to start writing the method section of the thesis report where I describe the method and how the original problem was solved, but I have no real theoretical background/models except for the ones that the authors of the previous articles wrote. How should I reference these things? I still want to show the logical evidence and models that they use without plagiarizing their work. Can I use the same/similar pictures/models/evidences in this section of my report and just refer these things to the original authors and their report? Should I mention it in the beginning of the section that all of the models are from the original authors?