convert Image to InputStream or FileInputStream

[val george]

Hi everyone,
I tried really hard to solve that problem myself but not much luch so far.
If anyone could give me a hint how to convert an Image into an InputStream or FileInputStream I'd would greatly appreciated.
I need to do this manipulation cause I decoded the image file in order to change the size but now I have troube when I try to incode back the Image into a jpeg file again.
Thanx in advance.