Is there any way to seperate astronomical and instrumental objects? Here is a image of hcg79 taken from APO. I'm just curious if there is any way to seperate astronomical and instrumental features in this picture? Thank you.
A priori it is very difficult to distinguish the origin of any particular feature from just one image.

For that reason it is established workflow, especially in astronomical context, to create 4 kind of images:


the light frame R. That's the actual image of what you are interested
in 
the dark frame D. That's an exposure of identical length and at
identical conditions, but with closed apperture. That takes care to
assess the sensor reading in the absense of anything visible
the bias frame B. That's a short-duration image which allows to assess the
read-out noise 
the flat field F. That's an image of a perfectly white /
grey area which allows to assess the different sensitivity of the
individual pixels.


Then you can obtain the corrected image C via $ C = (R-D-B) \cdot \frac{&lt;F - D - B&gt;}{F - D - B}$

https://en.wikipedia.org/wiki/Flat-field_correction