Want to spice-up your course Overview page by displaying image thumbnails in the lesson boxes? This doc will assist you in adding photos to the lessons on the main page of your course!
While Teachery lessons aren't designed out of the box to have image thumbnails on the Overview Page of your course, you can accomplish this very easily:
Step #1: Click into the Lesson you want to edit (from the editor sidebar on the left)
Step #2: In the "Lesson Title" field you'll want to add an image below the Lesson Title text (or you can remove the text if you don't want text).
TIP: Once the image is uploaded, click the image and use the Style button, and set the image to Full Width to fill the entire area nicely!
Step #3: Click back to the Overview Page of your course OR click the "Preview Course" link in the top left of the sidebar to see your course Overview Page in action!
If you do NOT want any text in the Lesson Preview boxes, ONLY IMAGES, simply delete the text above the image and you'll be left with just images.
That's it! 
Advanced Tip: Don't want to display the images in your lessons? If you ONLY want the preview image to display on the Overview Page of your course and NOT in the Lesson itself, you can add a small snippet of custom CSS (below) to the Add Custom CSS area of your course (found in the Style Your Course > Add Custom CSS page of the sidebar editor).
#lessons-page .imitate-h2-template-2 img {
display: none;
}If you just want to hide the preview images from the "More in this lesson" box that appears in the right sidebar of every lesson page, you can use the CSS below.
#lessons-page #sublessons .toplist img {
display: none;
}