I can only say that twice in my internet experience I tried to report an incident to the legal authorities. The response was different in both cases.
In one, someone sent me a picture allegedly of him having oral sex with an obvious minor girl. The local police said they could do nothing since the pedophile was outside their jurisdiction and out-of-state. They contacted the FBI who came to my home and warned *ME* that if I had the "offending" picture on my computer and showed it to them, they would also have to arrest me for possession of child pornography!!! I did not show them but instead reported the person to Prodigy (my ISP as well as the pedophile's). Prodigy would do nothing without proof of the "offending material" but warned me that if it were, indeed, "child pornography" and I transmitted it to them, they would not only report the original sender but also have to report me for sending it to them as well. It was a no-win situation.
In the second, I was sent a series of photos of a pedophile in varous sexual activities with obvious young boys. I had his home address, telephone numbers, real name, place of employment, and everything else possible to identify and "capture" this guy. Again, the local police would do nothing since he lived in another country. The FBI, again, repeated their warning to me that my possession of the material made me a "child pornographer." I contacted the embassy of this man's country. They were quite interested in obtaining his information, which I gave them willingly, without any evidence other than my formal statement. I continued to see the man online and wondered if anything were being done. I contacted the embassy again and was told that they had investigated and that the "boys" were of "legal consenting age for sex" in their country so his conduct was not illegal in the country of his residence.
So, while I encourage people to report, it's not so easy as one may think!