MSimg32.dll is a component of the Microsoft Graphical Device Interface (GDI). GDI is the tool Windows uses for drawing lines, boxes, text and other basic elements of the user interface. GDI was introduced in Windows 95, and extended over time. MSimg32.dll does not contain the core functionality, but it does hold three of the extensions.
GDI was depreciated with the release of Windows XP, but it is still distributed with newer operating systems, including Windows 7. Because of this, problems with MSimg32.dll can still cause problems on newer systems.