You don't.
The intent of newsgroups (other than those that have the word "binary" in
their title) is to use text only. Binary attachments are discouraged. You
need to recognize that these newsgroup have world-wide participation. While
high-speed connections are common and inexpensive in North America, that's
not the case everywhere. You'll find people using dial-up to participate in
the newsgroups, plus people getting charged by the minute for their
connections. They definitely wouldn't appreciate the overhead of having to
download binary attachments.
Describe your situation in words: that's usually sufficient. If it's not,
find a website where you can post the pictures, and include a URL to that
site.
