Remove the cursed 'invisible' rectangle background from a TIFF bitmap.

Hi everyone

Not even a brick of Semtex will remove the 'invisible' rectangle background of a TIFF bitmap. (I'd like to remove the middle bit as well, and assume the solution will work for any area ...)

I've googled and searched but nothing suggested seems to work for me. For starters, no matter how I much I beg,  I can't persuade the magic wand in Paint to make those mask ants.

Any simple suggestions for the simple-minded - that being me?

Thanks
Mulberi