A clumsy way would be to copy from each cd into a single folder on HD
Each time a duplicate appeared you would have the flag about do you wish to overwrite the existing file?
2 obvious snags:
1) If you saved different images at different times but happened to use the same name.... you would "lose" one or the other.
2) The result would be that all the files would now be in one folder. Making subfolders first would defeat the object.