Hey @Vasiliy, 

Do you mean to ask if it was possible to use a specific pixel tracking to validate if a contact as opted into your list upon opening an email as opposed to using the standard Double Opt-In Process of confirming one’s subscription via a button click?

If so then it would not be possible to replace the Klaviyo Double Opt-In Confirmation process with only a pixel tracker as a substitute as this does pertain directly to one’s consent to join a list. 

Furthermore, so long as Double Opt-In is enabled on the list you are adding customers to, customers must adhere to this setting of confirming their subscription via the Confirmation email sent to these contacts in order for these contacts to share explicit consent and be added to the designated list. Contacts who do not confirm their subscription to the list would still have a Klaviyo profile created; but not added to the list. 

-David