File manager that compares thumbnails

Dear experts,

I need to merge thousands of images files from several folders into one large folder. Many filenames are identical, but the underlying images may be identical or different. I will have to compare thousands of images, one by one, and decide case by case if I want to replace the existing file or not. Finder only asks me "The filename already exists. Do you want to replace file A by File B?" without showing me the thumbnails of the files. How do I know if I want to replace without the preview? No way.

I need a file manager that would compare the previews of the image files and their properties, like this: http://kobzar.be/objects/do_you_want_replace_file.png

Could somebody advise a file manager that has this feature, please?