As I understood from your question, you have to see what is your view? you may use basic features to describe characters then it most likely is not linear! I mean you need to see how you would describe the data?

But in general it is very, very difficult to assume that such data are linear because of human behavior on writing like hand speed, writing style, spaces between characters and a lot of other issues. Just for your info, handwriting is Chaotic phenomena which means it is not linear.

Thanks for your interest but my question is still unanswered!  Actually I know that certainly my data is non-linear.  I know that features extracted help me to recognize my data. But my question is ' how to see that my data is non-linear? ' - Can I plot it, rather if I plot then what exactly I plot ? I have features say 100 then how do I use them to know my data pattern- linear or not linear???

well what is linear and what the non linear phenomena is?

If your extracted features have linear behavioral that you can predict them for bigger size or much features, it is linear otherwise no.

I think you have to show (plot) features such a way that shows this fact. e.g. Matlab has various plot for such aim. This is important that you find a meaningful feature.

Let we consider geometric feature (e.g. size of chars) then show (plot) your data info based on such feature. You can see on the plot if they are linear but (at least) I don't know any features that can linearly describe characters well.

good luck

Thanks.