How to find the active image?

I receive this error: “the active image does not have a selection”
as there are multiple images open, I need t find the active image and select it to solve the error.
Any idea to find the active iamge?

The error message does not indicate that you need to select the active image. What it does tell you is that you have no selection as in a region of interest on your image. This happens when you want to use a tool that requires a selection on the image to work.

The active or current image is the image which is currently in front in ImageJ. You can get the title of said image by getTitle(). You can bring any image to the front by using selectWindow(“Name”) or selectImage(id). You can check if an image is active by isActive(id) etc…