I've seen someone adding pictures to the modules, so that students can view the homepage with pictures for each theme/week/module.
I've seen someone adding pictures to the modules, so that students can view the homepage with pictures for each theme/week/module.
Hi Hanna van Dijk 
However, what the rest of your question describes--it seems to me--is the fact that an instructor created a page that happened to have images on that page to a module. That is something that is done much more frequently and something that (in my opinion) looks much better than simply uploading just an image file to a module.
Any existing page can be added as as a page to a module, and that page, in turn, can also be set as the course home page (How do I set a Front Page in a course? ). But what many instructors do--and it sounds like this is the example you mention--is create a new page for each Module that functions as that specific week/module's "home page"--not the coursewide home page, but a "home page" for that week's module. And that is a great idea and one that is often used in many courses. It's simply a matter of creating a page (How do I create a new page in a course? ), and then placing that page within a module, which the first link I note explains in more detail.
You may want to check over all of the various features of Modules, in fact, from the Canvas Instructor Guide - Table of Contents . There's a whole section devoted to them!
I hope this helps a bit, Hanna, and that I understood your question correctly.
As Ken Black mentioned, you can have images on your homepage that each link to a different module. Is this what you are looking to do?
To do this, you can create your images (I love using Haiku Deck) or find images you'd like to use, then upload them to your homepage using the rich content editor. Then you can turn each image into a hyperlink to the corresponding module. Here is the Canvas Guides page about creating a hyperlink to other Canvas content (the page shows how to turn text into a link to a page, but you'd turn an image into a link to a module with similar steps).
Here is my example, where students could click on the image for a given unit to be taken to the module associated with that unit:
Good catch, JENNA TOWNSEND. Now that your reply led me back to this question, that may be exactly what Hanna had in mind.
This is great, thank you Ken Black and JENNA TOWNSEND! You've been very helpful. I've now succeeded in adding a page to my module with pictures and hyperlinks on it. Can I do the same for my course as a whole, i.e. adding a page that can be used as the homepage for my entire course. So that students can click on the different pictures that link them to the different modules?
Thank you in advance!
Best,
Hanna
Hi Hanna - Yes; definitely. Create a page that contains all of the elements that you want on a home page. Publish it. (That's important to be made into a Home page!) Then, follow the instructions here: How do I set a Front Page in a course? to designate your new page as a "front" page. Finally, head to the existing Home page, and specify a "Pages Front Page" as covered here: How do I change the Course Home Page? The page that you had previously designated as the front page will appear in the dialog box in italics. Presto! A new home page that you designed.
I hope this helps, Hanna.
Definitely helpful - it all worked out. Many thanks!
Hi Hanna - Yes; definitely. Create a page that contains all of the elements that you want on a home page. Publish it. (That's important to be made into a Home page!) Then, follow the instructions here: How do I set a Front Page in a course? to designate your new page as a "front" page. Finally, head to the existing Home page, and specify a "Pages Front Page" as covered here: How do I change the Course Home Page? The page that you had previously designated as the front page will appear in the dialog box in italics. Presto! A new home page that you designed.
I hope this helps, Hanna.