Sony Ericsson S710a

Is there anything special to keep in mind when adding a pic for a contact? I've had a little trouble when trying to use a picture that I have sent to phone from online. I've also transfered the pic using the memory card (it's a jpeg). The picture displays under picture for the contact, but does not display when the contact calls or when I call them. I tried using the same picture for another contact and it worked. Not sure if I did something wrong, or if there was anything special to keep in mind when adding a pic for a contact. Thanks.