Well... I just checked them, and sf::Image::~Image() is undefined inside libsfgui-s-d.a like it should be.
You must be doing something wrong during linking. Can you post your build log during a full rebuild for us to see? It would help.
And by the way... you uploaded libsfgui-s-d.a whereas your linker error refers to sfgui-s-d.a, in case you haven't realized.