Hi, when I uploaded this image on a social media site it had this blurry mirage-like pixels around the shrimps. I am not sure what is causing this, because when I viewed the image in my pc it looks crisp and not like this. What seems to be the problem? Is it the way I saved it from photoshop? Or the website just decompresses images so It doesn't look like how I want it?
There's plenty of JPG compression artefacts. Who has made them? Maybe you, if you have saved as JPG and used high compression (=low quality level). The website can increase it when it tries to make files smaller.
High contrast edges are especially sensitive to get those artefacts. A little blurring reduces them.
The website can have some recommendations how to retain the quality. See them.