The FileReader web API enables you to make local files available to content running in the browser. This entails a file picker and, depending on the verbiage in your browser UI, that may talk about "upload." That doesn't mean anything is being sent anywhere. See MDN: https://developer.mozilla.org/en-US/docs/Web/API/FileReader

(Or that nothing is; I have not audited this code. But I vouched the parent comment to point out that browsers do offer this capability, and there's nothing facially suspicious in claiming to use it.)

Images never upload to any server, all images processed in your browser