Could not load assembly ImageProcessor

Scenario

We have been use ImageProcessor nuget package for 4 years. We have not changed its version so it is still 2.5.2.

Problem

After last build we have noticed that when we want to add picture to our system (ImageProcessor is used there to resize pictures) we recieved runtime error:

Could not load file or assembly 'ImageProcessor, Version=2.5.2.0, Culture=neutral, PublicKeyToken=null' 
or one of its dependencies. A strongly-named assembly is required. (Exception from HRESULT: 0x80131044)

Tries

I have read article and found out that reason could be:

There are many reasons for this. In my case, also maybe in most of cases, the reason is the lack of signing which is the basic for strongly-naming. In VS2017, a signed project will become strongly-named automatically. To sign a project, a key-pair is needed. Hereby is my solution.

I am not owner of the nuget so I am not able to sign the nuget. I am not sure if it is real exception reason. Any help?