# Image Comparison Features
This article describes the set of image comparison features available in Appium. These features are available in all drivers and require OpenCV 3 native libs. Also, each feature is able to visualize the comparison result, so you can always track what is going on under the hood to select optimal matching parameters to achieve the best comparison results.
## Prerequisites
- OpenCV 3+ native libraries
- [opencv4nodejs](https://github.com/justadudewhohacks/opencv4nodejs) npm module: `npm i -g opencv4nodejs`. By default the preinstall script of this module also downloads and makes all the required OpenCV libs from source, but this requires developer tools to be available on the host system.
- Appium Server 1.8.0+
## Purpose
Image comparison might be handy for many automation tasks. For example:
- It is necessary to figure out whether the given picture example is present on the screen
- It is necessary to calculate coordinates of some predefined on-screen object
- It is necessary to verify whether the current on-screen object state is similar to the expected state
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