InvisiLetter API


Invisiletter API provides images which are embedded the digital watermark as well as InvisiLetter. The digital watermark can be extracted by using InvisiLetter and InvisiReader.

How to use this API

Send the URL – – containing query parameters.

Required Parameter

signimage : The URL of a sign image.This image should be JPEG/PNG format and grayscale (recommended 1bit) image under 512KB.

origimage : The URL of an original image.This image should be JPEG/PNG format and color image under 512KB.

Optional Parameter

strength : Number within the range from 1 to 255. Default is 60. If you specify small number, the quality of the embedded image is better, but the quality of extracted secret image is low.

requesturl : Specify “true” or “false”. Default is “false”. If you specify “true”, you can get an XML including the URI of the embedded image. Else if you specify “false”, you can get the embedded image itself.

Returned XML

If you specify “requesturl=true”, you can get an XML like below.

    (URL of the embedded image) 

If there are some errors, you will get an XML including error code like below.

errorcode 901 : the URL of signimage is invalid or too large to read.
errorcode 902 : the URL of origimage is invalid or too large to read.
errorcode 903 : origimage is not PNG/JPEG format.
errorcode 904 : signimage is not PNG/JPEG format.

(Example of returning errorcode 901 and 902 at the same time)

            A signature image cannot be read. 
            An original image cannot be read. 

Example of URL

About embedded images

The origimage will be resized 480×320 or less. In the resize of origimage, the aspect ratio (fineness ratio) is maintained. The signimage will be resized to the same size as resized origimage. In the resize of signimage, the aspect ratio (fineness ratio) is NOT maintained. The embedded image becomes the same size as the resized origimage.

For example, when size of origimage is 1024×1024 and size of signimage is 800×600, then origimage and signimage are resized 320×320 and you can get the 320×320 embedded image.

Format of the embedded image is full color PNG.

Original Image

Original Image

Secret Image

Secret Image

Embedded Image

Embedded Image

Extracted Image(by using Invisiletter/InvisiReader)

Extracted Image(by using Invisiletter/InvisiReader)


origimage, signimage and embedded images’ name are changed at random and it is preserved for a certain period in the server. Even if these images leak due to an unexpected accident, we cannot assume the responsibility at all. Use on acknowledging it and EULA.

It limits it to the non-commercial use. Please contact us when you use this to the commercial use.

End User Licence Agreement

This application program (hereinafter referred as “the Program”) is a computer application program provided by samurai-apps. You cannot download and use the Program without accepting the terms and conditions of this End User License Agreement (EULA). This terms and conditions of this EULA shall apply to all of the services in accordance with the Program. When you start using the Program, it is considered that you accepted all of the terms and conditions.

1. No Warranty.
the Program and other information is delivered to you “AS IS” and with all faults. samurai-apps do not and cannot warrant the performance or results you may obtain by using the Program. In the event that you or your computer devices suffer from any damage by using the Program, neither samurai-apps nor other companies will be liable for the damage.

2. Transfer.
You may not rent, lease, sublicense, assign or transfer your rights in the Program, or authorize all or any portion of the Program to be copied onto another user’s Computer except as may be expressly permitted by this agreement.

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All the rights in the Program are owned by samurai-apps. You may not copy, license, transfer or distribute the Program to any other person than you.

4. Privacy
You acknowledge and agree that the Program use the information (including your images) in the database managed by the Program to store it to any local or remote storage through network connection, only as and to the extent necessary for the Program to achieve its functionality.

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Under all conditions, we can stop distributing the Program at our sole decision.

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Upon your acceptance of EULA, it is considered that you agreed our changing the terms and conditions of EULA at any time without your separate acceptance. When such changes are made to EULA, you shall be bound to the updated version.

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