The answer of the above mention user helped me in understanding chemical reactions in a magnetic field, this is not the first time someone is profiting from SE, but I will reference the source appropriately, I would like to ask you what is the process of the picture, image copyright published on this website because the answer include the image that I will reuse and the publisher asked me to obtain permission.
We cannot tell you what citation style to use (e.g. ACS or APA). That is up to you, or whoever is in charge of your work, to decide. The only thing that is required is that, regardless of what citation style you use, please:
Provide a direct link to the answer in which this image is posted (in this case, https://chemistry.stackexchange.com/a/55482/)
State the author's name and provide a link to their profile (in this case porphyrin: https://chemistry.stackexchange.com/users/30424/porphyrin)
This is explained nicely in the link that Andrew T. already gave you: https://stackoverflow.blog/2009/06/25/attribution-required/
Whatever citation style you are using, there should be very straightforward ways of inserting this information into your citation. If you cite a webpage, you will have to provide the URL anyway, and porphyrin's username and link can go into the author field. Thus, these requirements are not really much more than the bare minimum.