some net sites and some e-mail have a black square with a red x in it
instead of the photo i'm supposed to see. how do i un-block this to
see what what i want or what i've been sent ?

It's not that the image is "blocked" but that the link it refers to
doesn't exist. You'll probably find that the images in the emails
aren't attached images, but linked images to some resource on the web
that is no longer there. You can sort of compare it to a 404 error for
a web page.