Ok here are some examples on this site I'll go through each from top to bottom and list my comments and questions.
http://www.dudeman.net/siriusly/ufo/art.shtml
1.) ~ "The Baptism of Christ" ~ 1710 AD
In my opinion this painting could depict a parting in clouds where the sun is shining down on the main characters.
But looking at the detail the artist put into the rest of the painting I find it odd that this ray of sunshine or moonlight looks so poor.
Given that this was painted well after the "birth" of "Christ" I could be just a silly theory the artist had like many people do nowadays about why Christ was so significant.
2.) "The Crucifixion" 1350 AD
This painting I do find interesting because yet it was painted well after the time period of the so called crucifixion the artist included a two passenger vessels in the sky one chasing the other. Obviously the artist intended it to look like a chase because the person in the vessel on the right is looking back.
3.) ~ "The Madonna with Saint Giovannino" ~ Late 1400's AD
Another religious painting.... with an object over the right shoulder of Mary and a person cupping their hand over their brow to either look at the object or look at Mary.
4.) ~ "The Annunciation" ~ 1486 AD
Another painting that shows an oval in the sky with a ray of light coming down from it but this time to a single point. Could be an interpretation of the parting of the sky with light coming down from it but like the ~ "The Baptism of Christ" ~ painting the rest of the painting is so detailed why would the artist choose to lack so much detail in rays of sunshine?
Perhaps this painting influenced the artist who painted ~ "The Baptism of Christ" ~
5.) "Glorification of the Eucharist" 1600 AD
I don't see how this could be construed as a satellite when it clearly looks like earth to include an orbiting moon. Obviously I think this artist was trying to depict "Jesus" and "God" painting the earth.
Seems like a very far reach to think of this painting as a depiction of an alien craft.
6.) ~ "The Assumption of the Virgin" ~
The "saucers" in this picture look like altocumulus standing lenticuler if they were meant to be an accurate depiction of clouds.
Although it seems in this painting the artist used the clouds as filler and more or less focused on the people in the sky and on the ground. The background terrain doesn't seem to have much focus on it either. So I think these saucers are definitely supposed to be clouds. They were not a focal point as in ~ "The Baptism of Christ" ~ and ~ "The Annunciation" ~
7.) Painting on Earls D’Oltremond's wooden drawer.
Well, the bible has a story of fire falling from the sky (meteorites anyone?) so it only seems fitting that this artist would try to include something along those lines rather than something from out of this world.
I interpret it as the artist wanted to depict Moses as pleading with God asking him to stop the wrath because he will show the people the commandments and they will obey.
8.) Notabilia Temporum -1465 AD
Some kind of ornament or symbol and a burning stick or symbol maybe to show two opposing sides? Or simply something else I don't know, but I do not think these represent spaceships!
9.) Ancient Mandarin Chinese painting - No idea on time period
Chariot with people in it, but in the sky..... The vessel looks like nothing that an ancient era couldn't have seen traveling on the ground but the artist put it in the sky. No big deal either way, it’s just a vivid imagination probably.
10.) The Magnificat and the painting just below it... - 15th century
Yes the object does look like a hat and is obviously contrasted against the rest of the skyline which indicates to mean the artist either intended it to stick out or he made a mistake and covered it up in a poor fashion.
The styles of both paintings look very similar so I think they could have been painted by the same artist or one artist mimicking the other. If it were the same artist it could have just been a signature in most of his or her paintings.
But it certainly does not look like a cloud simply because in the top painting it contrasts the cloud looking white clouds. In the bottom painting there are black clouds that have shade and detail while the hat looking object looks very out of place if it were meant to be a cloud.
11.) ~ England UFO Sighting from 1742 ~
If this is indeed a real document, I think it is very detailed in the description of what this person saw or thought he saw which does seem very interesting. However the Chinese invented fireworks back in the 8th century A.D. Although it seemed to travel very slowly unlike many common flying fireworks.
What I find even more interesting is the person’s comparison to objects that were common to the time but definitely perceived as very mysterious.
UFO sighting from Windsor Castle - August 18, 1783
Seems like a meteorite to me even in its description. But it was claimed to stop and change direction which is an attribute not often associated with meteorites burning in the earth's atmosphere.
13.) 17th Century fresco depicting the Crucifixion of Christ,
Looks like faces meant to be looking down on the crucified person. To me it doesn't seem mysterious it just seems to me that the artist wanted to make the faces look simple. Maybe the artist couldn't fade the faces into the skyline the way he wanted to so he chose this as an alternative?
14.) "Le Livre Des Bonnes Moeurs" by Jacques Legrand, 1338 (left).
At first I thought hot air balloon but after a little research I found out they were not invented until 1783 by Jacques and Joseph Montgolfier. Then I thought maybe a makeshift balloon? But what would have kept it airborne back in 1338. What’s with drawing all the gold shiny objects around it?
Maybe it was meant to be the moon and the shiny things stars? At dusk?
15.)~ "The Miracle of the Snow" ~ - 1400 AD
Simply looks like an artist’s depiction of Jesus looking down from heaven.
16.) Illustration of a Nuremburg UFO sighting, April 14, 1561.
A meteor shower mixed with a tad of Picasso?
17.) "Prodigiorum Ac Ostentorum Chronicon" by Conrad Lycosthenes - published 1557
Looks like a neat little drawing but nothing seems to scream out weird. People have imaginations and they try to invent!
18.) Broadsheet picture by Samuel Coccius
Looks like the sun over powering the stars light in the morning. Making them vanish.
19.) This 15th century fresco from Kiev
Halos around the heads and the central person having more meaning to the artist so he made him cooler looking.
20.)UFO sighting over Hamburg, Germany ~ on November 4, 1697
The artist depicts 2 larger objects than the moon which is on the right which seems kind of odd.
21.) UFO Sighting over Angers France, in 842 AD
Meteorite or comet hands down.
22.) "Annales Laurissenses" - 776
Probably stars, but its weird because there are objects within them. Maybe planets orbiting the stars? It wasn't common knowledge at the time but people do have an imagination which is why it is common knowledge now!
But seems kind of borderline to me.
23.) "La Tebaide" ~ Academy of Florence, painted c.1460-1465 by Paolo Uccello
Looks like a rock on the hill. What a stretch.
24.) UFO sighting by two Dutch ships - North Sea, 1660
I don't know when this was drawn but it could be modern but the sighting old. I think the picture is fairly modern though. But the sighting report seems fairly interesting although I couldn't find anything backing up that this sighting actually existed, other than on wuwu sites like this one.
25.)"Summer's Triumph" ~ tapestry created in Bruges, in 1538 ~ Bayerisches National Museum.
Clouds, although they do look similar to the ones in "10." but they don't stand out like the ones in "10" however they were painted at around the same time. Maybe artists like to depict certain clouds as hats back then? who knows.
26.) burning wheel over Japan, in the year 900 AD.
Wheels are round and so is the sun. I think the artist is trying show what he thinks of the sun.
27.)Nankin, China ~ September 28, 1890
Bigger please.... Seems like a stretch.
28.)Haratonohama, Hitachi, Japan ~ 1803 The book "Ume No Chiri" (Dust of Apricot)
Interesting to me. Very interesting. Imagination probably but what sparked it to fall into this category.
29.) 10th Century Tibetan translation of the Sanskrit text "Prajnaparamita Sutra"
Portholes? Please...... it looks like a plain old holy hat!
Hats do like to move at the speed of the wind and sometimes the wind does make melodious sounds.
Huge leap........
30.) last one in the photograph.
Not enough information given and it doesn't look to mysterious to me. Just seems like this artist liked to depict different Gods to different places or things in the painting.