There seems to be a bug with the RadEditor "Find and Replace" feature. I have recorded a screencast available here documenting the issue and will also provide below the information written: https://www.screencast.com/t/MXFawxIPp
Expected: '<img' is replaced with '<picture'
Actual:'<img' is replaced with '<picture'
Notes:This seems to be an issue with encoding as < is a less than tag. As you can see in the video, I do not think there is a way to escape the character to allow it to be replaced correctly. If you have additional questions, please ask.