Quick Blog:

I have recently encountered this issue where in a plugin image was not transferred along with the plugin step in the deployment.

Cause:

The plugin step was profiled in the source environment and the solution containing it was exported and deployed to other org.

I have a feeling if your plugin is profiled, the image will not be taken to other environment. Obviously it was a miss from the developer but this is something new i saw.

Solution:

All i did was unregistered the assembly from target environment —> unprofiled the step in source system — >exported the solution again from source — ->deployed the solution to target.

Hope this helps!