How can I change a picture in pdf form to jpeg form?

Open it in any decent image editing program- Photoshop or Photoshop Elements if you have them, Irfanview if you need a freebie, then hit "save as" and choose jpeg and a quality setting. For your own files, keep it top quality (least compression) For web, "7" is fine.

I tried opening it with Irfanview but it says that there is a decoding error.

E-mail it to me and I can change it for you