Photos nowadays can have embedded information in them such as make and model, settings used to take the photo, etc. This can be good but also bad depending on what information is embedded.
Similar Track Changes in a document, it is very useful when reviewing and modifying documents but if the same document was sent to say a customer it may not be so great.
In photos there may be things like make and model of the camera. Fine nothing too revealing. Settings used such as ISO, exposure settings Geo-location, date and time, etc. Some images can even have high resolution thumbnails embedded in them.
A useful tool to see if any of these information are in your photos visit Jeffrey’s Exif Viewer