A group of Microsoft Products and technologies used for sharing and managing content, knowledge, and applications.
All of my images are in a Thumbnail Photo column and not in the "Attachments" column (your attachments column might be hidden from view). This recent change by Microsoft enabled my "Attachments" column which gave my new incoming photos the "Reserved_ImageAttachment...." name. By disabling the "Attachments" column, I'm back to what it looked like before. All new photos come in like they did a few weeks ago.
To disable the "Attachments" column, go to List Settings > Advanced Settings > select the "Disabled" under Attachments. When you go to Save, a warning will pop up that all your Attachments will be lost. This is only referring to the Attachment column and not your separate photo column. Your photo column will no be affected.
This meant I fixed the problem going forward so to fix the problem for all the images that have the "Reserved_ImageAttachment...." name, I disabled the Attachments column and then renamed the photos by first downloading each one, renaming them, and then re-uploading them back to the individual sharepoint rows. All is back to normal now.