Attaching vs. Embedding
When you create a post you have the option to attach a photo to the post:
Attaching an image is subject to some pretty confining limitations on size. You'll have to make sure that your image meets those limits before attaching. When you're embedding, the embed code takes care of the resize for you. It's much easier and preferable to embed. Attaching also applies pretty brutal compression to your images. Use attachments as a last resort.
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