Multiple imports of single image are allowed

[yinchuangsum]

Describe the bug Multiple imports of single image are allowed, but only one output will be generated due to repeated name occur

To Reproduce Steps to reproduce the behavior:

1. Import an image
2. Import the same image again, you will see two exactly same image in the image list
3. Do some labeling, and then export
4. only one output file generated for the image

Expected behavior Each image should only allowed to be imported once

Screenshots

Desktop (please complete the following information):

• OS: Ubuntu
• Browser: Chromium
• Version: 1.0.0, 1.1.0

Additional context Add any other context about the problem here.