I don't understand what your requirements are.
Do you want to have executable processes? or just the the diagrams for documentation purposes? You mention JPG and BMP which are image formats, but then you said that you don't want to save the flowchart in any image format.
I don't understand what this is: "Actually we want to show clicak guideline as a flowchart on web page" I'm guessing that is some kind of clinical flowchart for a patient, which makes me thing that you want to execute the process for each patient.
Define schema in XML file and render it as flowchart blocks on web page -> What exactly do you want to render?
After rendering user should be able to add and delete flowchart controls -> What do you mean by flowcharts controls?
Cheers