There are two ways to capturing screenshot from selenium IDE.
Please refer documentation
We are going to take screenshot of flipKart.com
We make one blank image file screenshot.png under C:/
Now open Firefox and start Selenium IDE.
Enter command to capture screenshot and enter file path as following and Run the test and verify image at image location.
Selenium IDE Plugins – ScreenShot on Fail (Selenium IDE)
A plugin for Selenium-IDE to automatically take a screen-shot when a command fails while running the test suite
Add appropriate file path in Change reports folder and click that icon before start execution of TestCases using selenium IDE.
This plugin automatically take image when any error fired or assertion fails and store image of that and save to file location.