Images become darker

[Alienmaster]

Expected behavior

When switching between images on the tagging interface every picture is normal visible.

Current behavior

When switching between some images in the tagging interface sometimes the image is getting darker and darker. If you click into the image it gets normal again. The gray taint from drawing a bounding box is getting stacked.

Steps to Reproduce

1. Open a dataset and choose and image
2. Choose random pictures (some are already tagged) and get a more and more darker picture

Context (Environment)

Google Chrome 64bit Windows 10 x64

Where does the issue occur?

• Self hosted instance
• Public instance (https://imagetagger.bit-bots.de)

If it is a self hosted instance, please provide further information

• Operating System:
• Python version: 3.6.8
• UWSGI version: 2.0.20
• ImageTagger commit or version: v0.6