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There is a size limt so you need to either reduce the size or the jpg quality. I think the file size limit is 3.8mb but may be wrong.

That is why most folks use a flickr account and link to that

Hope that helps
 
Quick way to resize is open a photo in Preview.
Click Tools -> Adjust Size

In the width/height - change the width number a little smaller than what is listed. The height should auto change to keep proportions the same. This will show you a new file size for the photo as well.
 
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