Currently when you copy/move an image file to another location with the same name, you will get the Confirm File Replace dialog. This also has the small thumbnails that you can hover over to get a slightly larger thumbnail. If you double click on the thumbnails or Right Click > View in Directory Opus, you can then view it with Directory Opus's Standalone Viewer. If you scroll, it will display all the other images in that same directory.
Suggestion: Could you possibly make an option (through the preferences so that people can turn it on or off depending on their needs) that allows the Standalone Viewer to scroll only between the two conflicting image files? I think that would be rather useful since now you can to have a "full" viewer that allow you to easily scroll back and forth between the two conflicting images. This is useful especially if the two images have some slight differences that you may not notice until you do the quick back and forth to compare them.