Every camera adds so called metadata to your images; it contains information like resolution, ISO-Speed, aperture time, etc. Depening on your camera model even the serial numbers of your camera and/or objective are being added.
Because of that you should either remove all the metadata or just parts of it.
See also Photography.
To remove metadata from your images you can use the following programs on Linux:
The manpage of exiftool warns to not remove metadata from raw files as those information may be neccessary to process the files. Only remove metadata from (copied) files you want to upload.
On Windows you may use Exiv-Tag-Remover.
exiv2 rm *.jpg
man exiv2 for more information.
exiftool -all= *.jpg
'man exiftool' for more information.