How to hide text in JPEG? How to read such a message?

Question

I understand that you can hide text messages in jpeg files. How is this done? When you come across such a composite file, how to read the hidden text ?

Answer 1

There are various ways of hiding text in a JPEG image. It also depends on what exactly you're referring to. Here are just a few meanings:
1) Captchas are dynamically-generated images with random, obscured text used as a Turing test, ie. to determine if the person entering the data is actually a person, or an automated routine (a robot). There are free Captcha libraries available in various server-side scripting languages, eg PSP or ASP.

2) JPEGs can have meta-data in them. Author info, year, copyright, description and comments. Just like MP3s have ID3 tags - same concept. Image meta-data can be edited in most decent imaging programs, eg. IrfanView.

3) Real cryptography. Yes, it's possible to hide messages, even complete binary files, in images that are neither visible in the image, nor are part of the metadata. Knowing how to inject such data into an image requires a programmer familiar with the file format. Since there are more or less infinite ways to conceal the data, you need to use the exact same method to extract the data, which usually involves using the same program.
See also: Hide-In-Picture - http://sourceforge.net/projects/hide-in-picture/

Answer 2

JPEG files are image files, as such they don't contain text files, or any other text messages.

If you refer to the alternate text:
eg:

In this case the alternate text is "description for my picture", this text only shows up if the picture doesn't load. You can leave the alternate text blank, however if the image is not just for decoration it is not a good idea.

There is another thing, which I think you may have benn referring to. Some people use images to display a certain 'fancy' text. For example headings (see http://www.csszengarden.com/ - all its layouts use this technique).

Basically, the header text exists, but it's hidden using css, and only the background image is shown.

How to read the actual text? By simply checking out a page's source code.

Now, if you refer to the fact that someone has changed a jpg file, so as to hide a text - you can't. A jpg file only stores the order that pixels should show up on the screen. It doesn't store information related to the actual information displayed in that image.

Answer 3

Hide Text In Picture

Answer 4

I guess what you are looking for is steganography software.

A company called Steganos sell this... sometimes copies are given away on computer magazine front covers or you can buy it from them (about $US 62).

This stuff 'hides' your information in a jpeg or sound or other file.

Answer 5

is there? from what i know, the text are embossed to the file... in your case, an image file. Meaning it stuck there, like permanent ink. The text are part of the image to begin with.

I would even like to know if there is a software that somehow remove copyrights tag on an image.

Answer 6

Are you referring to that image file that shows up when signing up for an account? or when yahoo verifies that you are not a spammer so these things show up once in a while especially when you are forwarding lots of emails?

If is hidden from spammers and thos who are doing multiple sign ups.

Answer 7

i really donno about jpeg.. but u can hide text or secret message in bitmap changing the bit pattern of bitmap file...

Answer 8

So you learn something new everyday.