I can sort-of help you with those pics.
First three pictures are standard Byzantine art and early Christian medieval art. Look for any Byzantine crucifixion art and you will always see the sun and moon on placed on the upper left and right. Like these ones.
They're not spaceships. Your first pic represents the Moon. Sometimes the Sun and Moon have faces, others there are angels and people inside the Sun and Moon and that gets mistaken as vehicles or UFOs.
The second picture is taken from the Annunciation (of Mary where she will have a child) painting by Carlo Crivelli. Not surprising the images provided are always crappy so people can't see what these "ufos" really are...
Closer look the 'ufo' are actually clouds with angels which is also available found in similar Annunciation art in the right but with clearer representation of God, clouds and angels.
Another famous 'ufo' art.
Baptism of Christ by Aert De Gelder. What they call UFO is actually a dove. Symbol of the Holy Spirit. If you're familiar with your Bible you'll know the story behind the painting but unfortunately some do not and they jump on the Ancient Alien bandwagon and the crazy stuff they feed on TV.
Madonna with Child with the Infant St. John by Sebastiano Mainardi. Another example of how a cloud many generations later turns into a UFO. It is taken from Luke 2. It's actually the story of Christmas.
See the shepherds from other paintings looking upward to the glory of the Lord stated in Luke 2. Not a UFO.
Australian aborigines call these things Wondjina. They're nature spirits. They look like typical Greys but do they have to? Myths also say the beings painted these images themselves. Pretty strange way considering they travel many light years away to just fingerpaint. Who knows?

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This picture seems fake-y to me.
Could be UFO but then again why does it have to be UFO when it could be something else closer to home? What if this is just a snapshot of a bigger picture? Where are the rest?
