Missing welcome image in NSIS/MUI2

Even with the guidance that Anders provided I could not get this to work. My problem was with the image itself.

These steps worked for me using GIMP 2.8.10:

• create an image using RGB mode (Image > Mode > RGB) using the appropriate size for whatever you are creating (164x314 for MUI_WELCOMEFINISHPAGE_BITMAP, 150x57 for MUI_HEADERIMAGE_BITMAP)
• File > Export as ...
• name your file with a .bmp extension
• click "Export"
• in the window titled "Export Image as BMP" expand "Compatibility Options" and check the box that says "Do not write color space information"
• also, in the window titled "Export Image as BMP" expand "Advanced Options" and check the radio button under "24 bits" next to "R8 G8 B8"
• click "Export"

Now recompile your nsi script and your installer should be using the image(s) you specified.

MUI_LANGUAGE macro(s) have to come after the MUI_PAGE_* macros in the source file

For other people like me with the same problem but (slightly) different solution:

Make sure you do have the MUI_LANGUAGE macro. (And as the real answer suggests, it must be after the page macros). If you don't include it at all, many things seem to not work, not only images, but even some texts, and so on..

!insertmacro MUI_LANGUAGE "English"