As it stands, your rules prohibit just about any photo taken after the late 1980s unless 1) you took it or 2) the photographer explicitly placed it in the public domain. This means that cute picture of you that your mother took of you 15 years ago is not allowed.

3) You must have permission to use the sigpic or the copyright law allows you to use it
4) The picture is of yourself and not taken professionally
5) The picture is professionally taken, not of yourself, and it meets the "most photography labs will copy it without a release because it is so old" criteria.

I would also encourage a model-release rule:
6) No recognizable pictures of people other than yourself without a model release.

I'm not sure what exactly rule #5 is, I think it's typically stuff older than 1978.

If you want a shorter version:

1) Nothing erotic.
2) Nothing that would get CBLF into trouble over copyright, model-release issues, or any other legal issue.

With an explanation of common issues for #2:

Explanation of copyright:
Almost all photos taken since the mid/late 1980s get an "instant copyright" that belongs to the photographer. You do not own the rights to pictures your mother took of your kindergarten graduation in 1990 even if you possess the negative. Any photograph marked "(c)" or "printed on professional paper" or with the name of a studio printed on it is generally still under copyright unless it is very very old, like 1950s or 1960s or older. CBLF is not too concerned with photos your mother took. We trust that she won't mind what her children do with pictures of themselves. Please do not use professionally-taken photos unless you are sure the copyright has lapsed or you have permission to make copies.

Explanation of model-releases:
A model-release is generally only required for commercial use. However, some people may object to having their images used in a forum such as CBLF. In general, if your sigpic has a clearly-identifiable living person in it besides yourself, get that person's permission first. At the very least, it is the polite thing to do.

Explanation of "other legal issue:"
If you know of any other legal reasons not to submit your picture, then don't submit it.