This post explains how to set a thumbnail image to AEM content project modules.
Step 1: Create a folder named "definition" under "ui.apps/src/main/content/META-INF/vault".
Step 2: Paste thumbnail image(.png) inside the created folder. Name of the image should be thumbnail
Step 3: Create a file ".content.xml" under definition folder.
Step 4: Paste following content inside the created file.
<?xml version="1.0" encoding="UTF-8"?>
<jcr:root
xmlns:vlt = "http://www.day.com/jcr/vault/1.0"
xmlns:jcr="http://www.jcp.org/jcr/1.0"
xmlns:nt="http://www.jcp.org/jcr/nt/1.0">
<thumbnail.png/>
</jcr:root>Step 5: Repeat the steps for all content project modules. Build and deploy the code. You should see a thumbnail for all the modules you made changes for.
Feel free check my git project in case of confusion:
