Ionlyprograminc

Pixel trackers are invisible images which are the size of a single pixel hidden within a given email (Not visible in most mail clients). These images are sourced from a unique url (unique per email address) which when accessed are tracked by the web service as a view of a given email from a given individual. These are usually used in marketing emails to see how effective their campaigns are.

more info @ https://en.ryte.com/wiki/Tracking_Pixel

DMARC feedback is only based on the MTA (Message Transport Agent) handling the mail. I don't have much experience with DMARC reports but Senders typically use it when they are first Setting up DMARC. It is up to the receiving MTA to send the inbox/spam result according to the RFC. I think that the reports are aggregated so single inboxes are not able to be detected. I don't think many people actually send / follow up on DMARC reports imo.

Source: https://tools.ietf.org/html/rfc7489#section-7.3

A message can still be considered a DMARC failure since the check depends on both SPF and DKIM. You can have various failures like recipient rewrites and general SPF/DKIM failures which will fail DMARC a significant amount of the time.