When you write a report, you don't just make something up.
You explore your subject, get inspired, and substantiate your choices. You build on ideas, theories, and research of others. It should always be clear what you have come up with yourself and where you use the work of others to support your own arguments.
That's why you should reference every text resource you've used in your work. This includes also images, videos, audio, statistics, diagrams, etc.
If you don't, it's plagiarism.
Plagiarism is an infringement of copyright and can have serious consequences, such as material and reputation damage.
By citing your sources you:
- show that:
- you are aware of previous and ongoing research;
- you have studied the subject in-depth, and have consulted reliable and authoritative sources;
- support your argument by referring to 'authorities': respected authors, scientific works;
- enable others to find the sources you have based your work on, for deepening or confirming your interpretation;
- make clear what your own thoughts are and what someone else's (academic integrity);
- respect the intellectual property of the creator.
By using and correctly citing relevant sources, you increase your credibility and thus the quality of your report.