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How to write hidden text into image

—= EXIF =—
Exchangeable image file format (officially Exif, according to JEIDA/JEITA/CIPA specifications) is a standard that specifies the formats for imagessound, and ancillary tags used by digital cameras (including smartphones), scanners and other systems handling image and sound files recorded by digital cameras. The specification uses the following existing file formats with the addition of specific metadata tags: JPEG discrete cosine transform (DCT)[1] for compressed image files, TIFF Rev. 6.0 (RGB or YCbCr) for uncompressed image files, and RIFF WAV for audio files (Linear PCM or ITU-T G.711 μ-Law PCM for uncompressed audio data, and IMAADPCM for compressed audio data).[2] It is not used in JPEG 2000 or GIF.

This standard consists of the Exif image file specification and the Exif audio file specification.

wikipedia
duck.png

there are many tools, in this post I will use exiftool Linux tool:

$ exiftool duck.png
ExifTool Version Number         : 11.65
 File Name                       : duck.png
 Directory                       : .
 File Size                       : 22 kB
 File Modification Date/Time     : 2020:03:13 05:49:30+02:00
 File Access Date/Time           : 2020:03:13 05:53:21+02:00
 File Inode Change Date/Time     : 2020:03:13 05:49:38+02:00
 File Permissions                : rw-r--r--
 File Type                       : PNG
 File Type Extension             : png
 MIME Type                       : image/png
 Image Width                     : 512
 Image Height                    : 512
 Bit Depth                       : 8
 Color Type                      : RGB with Alpha
 Compression                     : Deflate/Inflate
 Filter                          : Adaptive
 Interlace                       : Noninterlaced
 Significant Bits                : 8 8 8 8
 Image Size                      : 512x512
 Megapixels                      : 0.262

Let’s add some text “secret text for you 😉” into duck.png image metadata.

$ exiftool -Comment="secret text for you ;)" duck.png

Let’s check metadata again:

$ exiftool duck.png
ExifTool Version Number         : 11.65
File Name                       : duck.png
Directory                       : .
File Size                       : 22 kB
File Modification Date/Time     : 2020:03:13 05:58:51+02:00
File Access Date/Time           : 2020:03:13 05:58:51+02:00
File Inode Change Date/Time     : 2020:03:13 05:58:51+02:00
File Permissions                : rw-r--r--
File Type                       : PNG
File Type Extension             : png
MIME Type                       : image/png
Image Width                     : 512
Image Height                    : 512
Bit Depth                       : 8
Color Type                      : RGB with Alpha
Compression                     : Deflate/Inflate
Filter                          : Adaptive
Interlace                       : Noninterlaced
Significant Bits                : 8 8 8 8
Comment                         : secret text for you ;)
Image Size                      : 512x512
Megapixels                      : 0.262

As you can see text added:

Comment: secret text for you ;) 

In windows you can check metadata and it will looks something like this


You can save and extract Geo location lat & long from media files and more details too.

Note: most famous social media extract or removes(or in fact compress media files while uploading which cause exif data removal) but other many websites DONOT ex. flickr @_@

Understand Flickr EXIF data

EXIF data reveals the story behind a photo. Info like the camera type, settings, and location are automatically added by the device when it’s captured. You can see any photographer’s EXIF data if they’ve made it public.
Show or Hide EXIF data
– Click any photo to open it.
-Below the photo, click Show EXIF.

You can hide the EXIF data by clicking Hide EXIF.
Manage your EXIF data
– Keep EXIF data secret – Update your Privacy Settings to hide your own EXIF visibility.
– Missing EXIF data – Some image editing apps delete this upon saving.

https://help.flickr.com/en_us/understand-flickr-exif-data-r1ge02Xo1X

Which means if your smartphone camera enabled to save the Geo-location and you just capture video and upload it online.. that means your current physical Geo-location and more other details about you will be available online to the public.