It's more than easy.... (Provided you put in the effort.)
The computer hardware exists to do it, readily available and affordable. And if you have the extra money to spend and know a thing or two about
networking, getting a render-farm up to boost your production capabilty isn't that big a step either.
Readily available 3D software:
Blender, Carrara, Vue, Cinema 4D, Lightwave, 3DS Max, Maya, etc...
Readily available post production & editing software:
Premiere, After Effects, Sony Vegas, Wax, Virtualdub, etc...
Yet now that tools for fakery are within the common domain, people still try to make claims about this or that. You really can't easily prove it's
authentic by saying "Hey look! There's a shadow!"
Guess what, unlike some years back the software these days has the tools to make compositing look good. (Even cheap or free like Carrara and Blender.)
So you can make an approximate rough model of the scene, make it a shadow-material that doesn't render as visible except for shadows, set up the
scene lighting to be close to the conditions in the composited video, and boom! You've got a shadow from the faked object(s) that closely matches
what would occur in the lighting of the real video as it projects onto the shadow catcher so that it appears to be falling onto terrain and buildings.
Other things like appropriate reflections can also be composited in too, if you're picky or clever enough about doing the effects work.
And with post-filters in the video editors, you can't honestly separate objects from the scene by contrasting noise artifacts. If you intentionally
add some video noise filters or enough compression - the artifacts are going to be consistent through the whole video. So that supposed tool for
proving realness becomes useless as well.
And then with things like LEDs and LED related novelties like party-blinkers, various laser show kits, micro R/C, cheap mylar balloons, gliders and
kites, chinese sky lanterns, etc. it's also quite possible to do some fakery the ol' fashioned way. Put some magnetic multicolor LED blinkies on a
balloon or kite, set it aloft, and it's not that hard to let the fun begin. If there's a haze in the sky at night, lasers become an interesting
option too. And if you have enough big money to spend, there's also optics that can rapidly adjust the focal plane of how lasers project. Thus the
distance of the brightest point can be controlled, and with a thin cloud to project into - it can produce a 3D holographic effect. (3D laser
projection is still a fairly new tech, but if you look hard enough you can find examples.)
As neat as it would be to see something real, it's becoming harder than ever if not impossible to prove it.
So why do I still bother to follow what goes on with UFOs? The topic is still interesting because the phenomenon dates back to before fakery was as
easy, the stories are interesting, and the ideas of beings from elsewhere actually wanting to visit this planet while bringing along novel
technologies are fascinating. Some aspects seem strangely plausible enough that there might be a grain of truth in some stories or sightings.