Evidence we need
- Images taken by the aliens of their own homeworld.
- A sample of alien DNA (or the equivalent).
- Emission spectroscopy of the light emitted by the UFOs
- Exotic material never yet produced on Earth, perhaps as part of "UFO" wreckage.
- A mathematical proof which would be quite routine for the alien but which has not been solved by us on Earth at this time.
- Similarly, any technology or scientific theory - unification of quantum mechanics and relativity would be nice.
Evidence we got
- Blurry pictures of hubcaps captured mid-toss.
- Unsteady handheld video of some lights floating in the darkness which could well be the parking lot of a desert roadhouse a half-mile away.
- A black dot seen in two frames.
- Anecdotes and stories - but never photographic evidence - of closer encounters with spacecraft.
- Pictures created by a "how to make your own UFO" guide.
- Project Blue Book, cataloguing every UFO story anyone bugged the USAF with for eighteen years and listing why pretty much every one was conventionally explicable.
Conclusions on evidence
Now with the wide spread of cheap mobile phone cameras, high quality point & shoot cameras, as well as cheap, high definition handheld recorders an influx of much clearer and well-focused, UFO recordings are expected. Any time now. Aaaaaany time now... indeed, the quality of UFO evidence has not increased with the technological ability to capture it.UFO proponents usually defend the lack of evidence based on a form of special pleeding for UFOs. Perhaps science shouldn't discount eyewitnesses, no matter how drunk, or should drop some of its intellectual rigour for the sake of UFOs - say, to forget about reproducing any experiments, as most of the time no two UFO reports ever cite the same details with true independence.
http://rationalwiki.org/wiki/Unidentified_flying_object#Evidence_we_need