Online acceptance through email esign accepted for freelance contract

Hi, I am a graphic design, web design & development freelancer from Tamil Nadu. Before starting the work, I am planning to draft a contract between me and the buyer of my service stating quotation, payment details, schedule time of delivery and other legal clauses and get it signed from the buyer. Since my work is not location based always, I may get buyers all over the India or outside. I feel it is difficult and inconvenient for both the parties to courier the agreement for signature. Now, I wanted to know, if there is any legal option for getting acceptance digitally over email or through e-signature. Whether the acceptance provided by the buyer through mail will be legally accepted in case of any future dispute? For e-signature, a image of the signature is enough or is there any e-signature certification required? If online acceptance is legal, what are all the information I need to include in the agreement and what are the steps to be followed ? Thanks, Hariny