Python: Find brightest pixel in fits-file and ignore brighter artefacts
Following Mick's comment, I found an astropy-function - DAOStarFinder - that does what I was looking for. It scans an image for light-sources and one can set threshhold for a detection, e.g. the "roundness", "sharpness" or brightness of an object have to be between [-0.05,0.05], [0.6,0.8] or >5*standard_deviation, respectively. I must say, that I have the impression the roundness and sharpness measure don't work consistently and sometimes values for the same object change enormously from one frame to the other. But DAOStarFinder gives you also a rough estimate of the flux density of the object, which I could use for sorting the sources and filtering out the relevant one. Here is a link to example script and to the documentation of DAOStarFinder. And here the example script explicitly:

&gt;&gt;&gt; from astropy.stats import sigma_clipped_stats
&gt;&gt;&gt; from photutils import datasets
&gt;&gt;&gt; from photutils import DAOStarFinder

&gt;&gt;&gt; hdu = datasets.load_star_image()    
&gt;&gt;&gt; data = hdu.data[0:400, 0:400]    
&gt;&gt;&gt; mean, median, std = sigma_clipped_stats(data, sigma=3.0, iters=5)
&gt;&gt;&gt; daofind = DAOStarFinder(fwhm=3.0, threshold=5.*std)    
&gt;&gt;&gt; sources = daofind(data - median)    

&gt;&gt;&gt; print(sources)