receiving email “image_seo off”

I uploaded two images, one at a time, through Media Library Folders as follows:

I went to Media Library Folders and selected the folder.
I clicked on Add File.
I dragged the first file to the drag and drop area.
After the first one completed, I dragged a second file to the same place.
I got an email that said:

[09-May-2017 00:46:22 UTC] image_seo off
[09-May-2017 00:48:41 UTC] image_seo off

What does it mean? Is there a problem?

Last week I had uploaded other files in the same way and did not get an email.