I just encountered an issue with Zoho Show when I tried to upload an image file but since it didn't have an extension 'zShow' is rejecting it. I don't think it is a professional and secure way to depend on image files just by attachments as it would open up security holes and blow up the system.

On a typical cloud computing the server should basically check the header of the file and decide if it is a valid image. In a typical .NET parlance Image.FromFile should be able to decide a file as a valid supported image and/or throw an exception otherwise. I believe Zoho is a Java suite but there should be something equivalent available for you from the Sun (Oracle) world too.

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Deepak Vasudevan
http://thamizhththendral.blogspot.com/