I am making an application using Windows Form and it will be used on a tablet that mainly use touch/tap for input. Is it okay if I am using Image for buttons? Like using image for add, save, delete, load, show/hide label, etc. Can you give me a web or references for designing Windows Form UI?
This is a bit more of a coding & development issue than UX IMO.
Ideally you should try and use CSS/html/whatever you're using (not at all familiar with windows forms) to do it natively. Using an image for a button isn't good practice; it does have UX implications for accessibility (how does a blind person know that's what they've got to press?- hope you have a nice text label in the code) and it won't be great for people with slow connections.
It depends on the image. You don't just want a boring button with text, but at the same time, you don't want an ugly image. Try to stick to images for things such as add, save, close, etc. But keep it modern and 'nice' looking, making it very simplistic.
I have not worked with windows forms in particular, but a quick search told me that it is more accustomed to the desktop mode, like normal windows, than the touch friendly Win RT look. You can still develop desktop based UI as Windows 8 tablets will provide an inherent support for the same. I just wanted to highlight, that you might want to look at WinRT based UI approaches if tablet and touch is your primary consideration.
Considering your primary user is going to go with touch input, you'd want to keep an eye on the size of the image. It should take care of fat fingers and controls should not be placed very closely, else you'd have wrong actions trigger every now and then.
Also, a habitual user would be expecting buttons if he sees Windows Forms, so there should be strong reasons for deviation from customs. Also if you choose to use images you'd probably want to give special attention to affordance. Your image size, shape, color etc. should make it distinctively clear that there are actions to be performed on tap.
Currently your question talks about can you do it? and the answer would be yes, but for should you do it, we would need more inputs about the why part and what exact needs you are trying to meet.
I hope I have been of some help.