Hi Vidya,
There are a lot of factors that affect image comparison and may cause its failure. For example, the physical and virtual machines may have different operating systems installed on them. In such cases, images may look similar, but they still will be different for TestComplete. To avoid such situations, you can change the checkpoint properties so that TestComplete ignores a slight difference between the captured images.
There are some helpful links below that contain more detailed information on image comparison and the factors affecting it:
1. Why Image Comparison Fails
This topic provides information on possible reasons of image comparison failures.
2. Factors Affecting Image Comparison
This topic provides information on the factors that affect image comparison and may cause comparison failures.
3. Comparing and Finding Images - Specific Tasks
This topic contains information on how to make the comparison and search procedures "smarter".
I hope this helps :)
