Weekly Social Media Tip: Proper LinkedIn Posting
Upload and post photos directly to LinkedIn. Photos do not show up properly on the professional network when shared via an app such as Hootsuite or SproutSocial.
LinkedIn focuses on highlighting headlines rather than images. So you’ll have to log in to the professional networking site to upload images directly in order for them to appear correctly.
LinkedIn images should ideally sized 800×800 pixels.
Check out this social media image size chart from @KevanLee @Buffer.