Are those stars? The “iduy37thq” image [0], for example, has various star-like points of light on top of the planet itself in addition to appearing in the background.

[0] http://hst.esac.esa.int/ehst-sl-server/servlet/data-action?R...

No they're probably not (I'm an astronomer). They're likely cosmic rays. When I've used Hubble data, then the processing uses multiple images to remove the cosmic rays (which aren't in common between images).

I'd love to understand how those bright dots and lines (so, cosmic rays?) appear on these images.

They're just high energy particles that interact with the CCD cameras typically used for astronomy. You get a bright point or particle track, as the particle interacts with the CCD producing electrons. This is worse for space telescopes, as there are more cosmic rays in space. For some simple information see: http://spiff.rit.edu/classes/phys373/lectures/cosmic_rays/co...

This look like the noise I get from my camera when I take very long exposures (> 10 minutes). The sensor starts heating up and producing these dots.

I'm an astronomer, and I think you're probably wrong. It's mostly down to exposure. Those little dots you're seeing in the images are likely cosmic rays. Those are removed by combining multiple images, as cosmic rays don't appear in the same places.

The pixel-sized dots are cosmic rays, those are obviously artifacts as some of them can be seen in front of Saturn.

I'm referring to objects you can consistently see between different observations. E.g. this one around 1/2 a planet width from the pole you can't see observed from 2018-06-06 14:35:05 until 2018-06-06 14:46:35:

http://hst.esac.esa.int/ehst-sl-server/servlet/data-action?R...

http://hst.esac.esa.int/ehst-sl-server/servlet/data-action?R...

http://hst.esac.esa.int/ehst-sl-server/servlet/data-action?R...

http://hst.esac.esa.int/ehst-sl-server/servlet/data-action?R...

Although looking again perhaps that's a moon of Saturn's rather than a particularly bright star.

Not an astronomer, just an interested amateur. The few times I've been curious enough to look at the raw data behind these images I've found background celestial objects that are definitely edited out. That's understandable, the point is to show e.g. Saturn and not whatever background objects happened to be there at the time Hubble took the photo.

I'm just pointing out it's not all due to the light exposure.

Is there a good explanation/article about how they take/process these images? I would have liked it if they could have included a bit of text about why certain items were not in the picture/removed.