Clarifying how and what illustrations and images you can use for your class work, senior thesis, or first publication can be a challenging process. It can often seem like a moving target, as laws and policies can differ by intended use, by country, or by type of ownership.
Before using any image in an academic publication, you must determine its source and any use restrictions in place. Whether an image falls under copyright restriction or not, you must credit the source. If you are unsure about you can always ask your subject librarian, or your professor who can help you one-on-one.
The best option is to create or use an illustration/image that you create and therefore would own the copyright to yourself.