Because, by uploading a picture with your posts, you can track how many readers read the post by seeing Picasa's report on how many user saw uploaded photo.
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The Hidden G+ Photo Stats - How-To
We hope that this short G+ trick helped you to see how many people read your Google+ posts. Thanks to Trey Ratcliff for this useful tip. If you have any idea or questions, feel free to ask us via comments below. God Bless!!