I am sorry for misleading you in my last reply. The PictureBox value indeed cannot be a vector image. What I meant with vector images was using Shapes due to the fact that you can set the Rounding property for the Square shape.
I discussed the issue with our development team. The behavior is resulted by the incorrect processing of the transparent parts of the image by the PDF rendering.
To avoid this outcome in PDF rendering, I suggest modifying the corners' images. Remove their transparency and put as background color the background of the GroupHeader section. Then in the report, set only the Value of the picture box, without setting the Background Image property.
You may check the updated version of the top left image and the report in the attached archive.
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