A 1 pixel by 1 pixel transparent GIF image is inserted in each email sent through Amazon SES and includes a unique reference to this image file; when the image is downloaded, SES can tell exactly which message was opened and by whom.
By default, this pixel is inserted at the bottom of the email; however, some email providers’ applications truncate the preview of an email when it exceeds a certain size and may provide a link to view the remainder of the message. In this scenario, the SES pixel tracking image does not load and will throw off the open rates you’re trying to track. To get around this, you can optionally place the pixel at the beginning of the email, or anywhere else, by inserting the {{ses:openTracker}} placeholder into the email body. Once SES receives the message with the placeholder, it will be replaced with open tracking pixel image. Just add one placeholder, as only the first occurrence will be replaced, any remaining will be omitted.
The addition of this tracking pixel does not change the appearance of your email.
Open tracking is available to all Amazon SES users by default. To use open tracking, you must do the following:
For details about how to enable open tracking through a configuration set’s event destination, see Creating Amazon SES event destinations . You can use the pixel placeholder in SMTP email in such ways as formatted, raw, and templated email.
Learn more about how to Monitor email sending using event publishing .
参考：
https://docs.aws.amazon.com/ses/latest/dg/faqs-metrics.html#faqs-metrics-opens
https://repost.aws/zh-Hans/knowledge-center/ses-email-opens-clicks