Jpg img is crisp on my disk but distorted on server

Explain this :

I draw a logo with vectorial tools of Flash , exported this image as .jpg file , which appears to be a fine high resolution image when viewed locally from my disk ;

then it was transfered to the server , and as the image is visualized on line , it shows a bit distortion , as if it was saved with poor quality , high compression small sized file ;

That´s the 1st time I face this , can someone give me an explanation ??

Cheers