Flux is shuffling of position of website in the search engine. Flux meaning in SEO -"changing the position of keywords". The changes in existing algorithms of Google ranking parameter are the reason for website flux. When you observe sudden ranking fluctuation for your targeted keywords, that means something is going on at the back end of search engine and that is known as Flux.
Image sharing has nothing to do with SEO. It does not mean your search results will increase by sharing images. Yes, Image optimization will surely help to do better for crawlers. You can optimize images by compression image size, adding proper ALT tags etc. If you are creating meaningful images and sharing on social media where your niche people are, it can bring traffic to your website. You can try these popular platforms to share your images Instagram, Facebook, and Pinterest etc.
To share your website links and unique content on social media platforms are important but the type of social media depends on your business niche.
For example, if you are selling jewellery or makeup or fashion accessories Pinterest, Instagram, weheartit will be the best choice.
If you have SEO, software development, app development services to promote, Facebook page, LinkedIn company page, Twitter official account are the best choice.