[JD Mather]

Expand the sketch that has the image.
Edit the Sketch.
Right click on the image icon in the browser and select Properties.
Select Transparency.
Whatever pixel is in the lower right hand corner will be your transparent mask color.
Use bmp for best results or second choice png. Do not use jpg as it will change the mask pixels and not give good transparency.

Use Decal command in Inventor to apply to part face(s).

Of course you may need to edit the source bitmap in a bitmap editing software like MS Paint or better.

If you have trouble figuring it out attach the bitmap image here.