By default, Bootstrap 4 has various form features for radio buttons with images inline. Here HTML 5 has default validation features, However, for custom validation, we must use JavaScript or jQuery. The following approaches would help in the display validation message for radio buttons with images inline.

Approach 1: First wrap the Radio buttons and its label by using the form-check-inline class. Then add img tag within the above wrap after the label tag. Use default required validation by adding the required attribute of a radio button. Finally, display the message using alert class and trigger it with jQueries attr(), addClass(), and html() methods only if the radio button is not checked.