>>Is the Windows service code using the same .NET version (esp. System.Drawing.dll). If so then I guess it's down to stepping the code to determine where the results deviate.....
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>Each application is tied to the framework. The framework uses 4.0.0.0. Also, in each application, the reference in there is also 4.0.0.0.
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>Where it works, the Platform is set for Active (Any CPU). Where it does not, the Platform is set for Active (x86). But, I do not think that would be a factor.

I think that may be the problem - might be worth testing with same CPU.....

>As far as stepping down the code, the line DrawImage() is where the difference is. When that is executed, it resizes the image. So, this is calling .NET core libraries. I do not know if that is traceable.