Https://splashsnap.com/ has been built to do exactly this. I've integrated it in iOS Shortcuts, meaning images can automatically be generated and set as wallpapers, all in the background! I've been waking up to a brand new wallpaper based off my theme preferences every day, and it's awesome. Let me know how you find it! Source: almost 3 years ago

Pattern Monster: A simple online pattern generator to create repeatable SVG patterns. Perfect for website backgrounds, apparel, branding, packaging design and more. - Source: dev.to / over 2 years ago

SVG Patterns (if it counts as illustration:) https://pattern.monster/. Source: over 3 years ago

For the back of the card I'll use and SVG pattern, feel free to use the one you like the most from Pattern Monster. Also center the background image with background-position, and make it cover the full card by adding background-size: cover;. - Source: dev.to / over 3 years ago

I'd like to put together a POC to show some possible solutions. I know there are some tools out there such as https://pattern.monster/ and https://haikei.app/ which can generate images, but ideally this would be a library or at least an API I can hook into, so admins can just create templates in our admin application without having to go to an external site and manually knock a thumbnail up. Although not required,... Source: over 3 years ago

Bonus points for adding a custom background - pattern.monster is a must-use, in my personal, humble opinion. Source: about 4 years ago