One of the best sites to use to find images for your assignment is through Creative Commons (CC). 
"Creative Commons is a nonprofit organization that works to increase the amount of creativity (cultural, educational, and scientific content) available in “the commons” — the body of work that is available to the public for free and legal sharing, use, repurposing, and remixing."
From: https://wiki.creativecommons.org/images/3/35/Creativecommons-what-is-creative-commons_eng.pdf
Using Creative Commons to find images
Type 'creative commons images' into the internet or go to search.creativecommons.org
Once on the homepage, choose from one of the search engines listed. For example, Google Images.
Type the image you are looking for into the search bar. For example 'Fauteuil chair'
The search returns will be directed through google images. Choose an image which reflects the furniture or piece you are describing.
Right click on the image and choose "save image as" to save the image.
Digital Public Library of America (DPLA) is another place to find copyright free images for use in assignments.
How to Use
Go to Digital Public Library of America and scroll down to find DPLA Images
Enter your search term into the search box and press Enter
Once you have found an image you wish to use click, on the title and information about the image will appear.
To save the image, click on the small image icon which will open a larger image.
Right click on the image and choose 'save image as'. Save the image as needed.
The Smithsonian is not as easy to use as either Creative Commons or DPLA, but it is still a excellent resource to know how to navigate.
How to Use:
Go to the Smithsonian homepage at www.si.edu
Click on 'Explore our collections' and enter your search term into the box on the top right hand side of the screen.
Press Enter and choose the most relevant return
If you need to narrow the returns, you can do so by using the "modify your search" menu on the left hand side of the screen
As in DPLA, to save an image, click on the smaller icon, and a larger image will load. Right click on the larger image and choose 'save image as'