Facebook has made Timeline available for everyone. One of the special thing about Facebook timeline is its Cover where you can show a quite large size of your picture BUT one must know how to choose the correct size of picture for Facebook Timeline. 850x315px (width x height)is the exact size for Facebook timeline. You should crop a picture to 850x315px to create a correct timeline cover.
What is the minimum width of the Cover Photo?
Its mentioned at Facebook FAQ that timeline cover image must be at least 720 pixels wide. Images with smaller size will get upload error. However, when i tried, i come to know that we CAN upload an image for cover at least 399px wide. So, if you upload 399px wide picture, Facebook will zoom this picture to fit in the timeline cover.
What if you use cover photo of any other size?
Well, Facebook would not allow you to upload any image below 399px however if you upload a cover photo of any other size, Facebook will automatically resize or crop the image to fit the picture into your timeline cover and you may see an out-of-pixels picture, so its better to choose cover photo with 850x315px size.
Can other people save Cover Photos?
Your Cover Photos are publicly visible and can be saved by anyone (friend, blocked friend, public etc). Actually, Facebook will only display a selected portion in Cover photo (which is virtually cropped) and whenever someone will save your cover picture, he/she will get the full uncropped image e.g. if you upload a big full size photo of yourself, and then decide to make the head as you cover photo, people saving the image can see the full image. So its a good idea to upload the exact size.