IDC_BUTTON は BS_BITMAP スタイルに

HBITMAP bm;

bm = (HBITMAP)::LoadImage(AfxGetInstanceHandle(), MAKEINTRESOURCE(IDB_XXX), IMAGE_BITMAP, 0, 0, LR_LOADMAP3DCOLORS);
((CButton*)GetDlgItem(IDC_BUTTON))->SetBitmap(bm);

::DeleteObject(bm);

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