The Forensic Science is the use of scientific instrument and procedures in the detection of crime pertaining to court of law. Use of Scientific instruments, procedures pertaining to detection of crime depend upon the skill and ability of the examiner.
In routine (Forensic Science) the document under examination may be forged or genuine depend upon matter under examination and expert is bound to examine the document very carefully and it is also the duty of the examiner to handle the documents with care so that the document should not effected in the course of examination.
The document may sometime contain detection of genuineness or forgery of the signatures because there may be genuine denial by the executants or the signature may be forged and its detection and examination should be made carefully and minutely by comparing with the sufficient standard signatures.
The forgery of the signatures are of many kinds and it depend upon the skill and will of the forger, how the forger forged the signatures because signatures may be forged by copied forgery or by tracing forgery or by impersonation.
The standard signatures for comparison may be taken from the case file and the expert should prefer to examine the signature as standard from service of summons and vakalatnamas because mostly these signatures are free from any intentional change and the signatures on the written statement or other documents written after denial may show intentional change.
The intentional change may or may not be present in the standard signatures. The intentional change will not be present in the standard signatures written by the executants after the denial of forged disputed signatures and intentional change may be present in the standard signatures written after the denial of earlier written genuine signatures by the executants and all these facts depend upon matter under examination.

Forensic Science Thumb impression comparison also require careful examination because comparison of the thumb impressions is made as :-
First the apex ridges are compared to determine as to if thumb impression under examination are of left hand or right hand.
If one set of thumb impression is of left hand and other thumb impression is of right hand, then these thumb impressions cannot be identical in any manner because thumb impressions affixed from different sides of hands even in the same person are always different.
When the thumb impressions under examination are from the same hand, then further examination of the basic pattern is made.
If the basic patterns are different, then it is a definite proof of non-identity and if basic pattern are same, then further examination of the ridge details is required.
The nature and position of the core point as well as delta point are also compared subject to their visibility because in the plain impressions, which are usually affixed, the delta points are not present.
The examination of the ridge detail is required when basic pattern is same and these ridge characteristics are examined with respect to their position/location and number of intervening ridges between them
When core point and delta point are clearly visible then the numbers of intervening ridges between these two points are counted and if ridge count is different than it is a definite proof of non-identity and if ridge counts are same then further examination of ridge details is an essential requirement.
If the thumb impressions under examination are partially affixed then the same can be compared with regard to their identity or non-identity depends upon matter under examination.

Sometime the signature/thumb impressions are lying on the blank papers and body writing is written/typed manually or with computer process and such documents falls under the term forgery over genuine signature/thumb impressions.
Such type of forgeries are detected by examining the document as a whole because such documents shows inconsistencies in the interline spacing, change in the vertical and horizontal alignment, adjustment of the description of the witnesses and their location as well as crossing of the strokes of the body writings with the thumb impression/signature of the executants.
The crossing of the strokes of the body writing with the signature/thumb impressions can be detected by Stereo Microscope and by making high magnification of the disputed portion depend upon matter under examination.
Sometime documents are also fabricated by lifting revenue stamps along-with the signatures/thumb impressions from one document to another document and such type of fabrication can be detected by examining the disputed document under comparison.
Age of the document cannot be determined directly from the examination of the matter of the document under examination but sometime there appears inconsistencies, on the basis of which the age of the document can be ascertain such as :-
If a document is of year 1940 or before it and bears writings with ball pen then it is a fabricated document because ball pen was not in use in 1940 as it was discovered later-on.
If a document is of year 1970 or before it and bears computer printing, then the same is also a fabricated document as computer printing was not in use in india in 1970.
If a document of year 1980 or before it bears a revenue stamp of worth Rs.1, then it is a fabricated document because stamp of Rs.1 came into existence in year 1994 as article 32 finance act.

Like these there may be some other basic inconsistencies in the document which can be detected by the examiner having knowledge of the subjection (Forensic Science) and one can detect the forgery in such manner by consulting with the examiner of questioned document. Sometime a document can be fabricated by transplanting signature/thumb impression or some other matter from one document to another document by trick photo-static technique along-with cut and paste method or by computer scanning process. In these types of fabricated documents there is no existence of the original and plea is generally taken that original is in the possession of opposite party or the same has been lost.

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