Here is what I think you are trying to do. The first step using DynamicCrop on the first image mark your area to crop and before executing drag the new instance triangle to the workspace. Step2 execute DynamicCrop using the Check mark. Step3 with the second image to crop, drag your DynamicCrop process icon that you created in Step1 into the second image. That's it. The process icon can be saved and used with any other image.
Mike