Query Strings ↗ are a simple, but powerful integration that allows you to generate dynamic images on demand by changing the query string of an image URL.
You start with a URL Base and construct the Modifications with strings of data according to your template's layers.
Check out How do I generate images using query strings? to learn more.
Note: Query Strings have now been succeeded by the more user-friendly Simple URLs. The functionality remains the same, but with an improved and more user-friendly method to construct modifications. Check out How to define modifications with Simple URLs to learn more about the new method.