nostra13/android-universal-image-loader

Android Universal Image Loader (UIL) is a Java library for Android apps that handles the common but tricky problem of loading images from the internet or device storage and displaying them on screen efficiently. Without a library like this, displaying images in a list or grid can be slow and buggy, images appear at the wrong time, memory runs out, or the app freezes while waiting for a download. UIL solves these problems by loading images in the background (so the app stays responsive), caching them, storing copies in memory and on disk so the same image does not need to be downloaded again, and letting you customize almost every aspect of the process. You can set placeholder images to show while loading, define what happens when loading fails, track download progress, and fine-tune how images are decoded and displayed. The library can load images from many sources: URLs on the web, files on the device's SD card, video thumbnails, content providers (the Android system for shared data), app assets, and built-in drawable resources. The API is simple, in the most basic case you pass an image URL and an image view and the library handles everything else. UIL is written in Java and supports Android 4.1 and above. Note that the project stopped receiving updates in November 2015, so it is effectively archived. It was an influential early library in this space, described in the README as "the great ancestor of modern image-loading libraries." You would encounter it in older Android codebases or use it as a reference for understanding how image loading works.