Whenever I include images or screenshots within the body of a blog post, I resize them so they aren't unnecessarily large. iPad Pro screenshots, for instance, are 2732x2048px and often larger than 1MB. There's no need to share these images full-size, so I reduce their dimensions to something like 1024x960px. This usually gets the file size down to around 200KB.
Back when I used a Mac to write blog posts, I would have also taken the step of optimizing the images using ImageOptim. This app uses clever compression techniques to reduce the file size while preserving quality. It was a simple drag-and-drop process that could drastically reduce the file size further. I haven't yet found an equivalent iOS app that does something similar, so image optimization isn't something I've been doing.
However, there are web services that perform image optimization. One such service, TinyPNG, has an API that can receive images and return a URL to an optimized version. Using Workflow's recent API support, I've created this workflow that both resizes and optimizes JPG or PNG images using the TinyPNG API. When the action extension workflow is run, there's an option to resize the image (using Workflow's built-in image resize action), after which it's uploaded to TinyPNG for optimization. An alert displays the difference in file size before the optimized image is downloaded. TinyPNG uses randomly-generated filenames, so you're asked by the workflow to specify a new one.
The following PNG screenshot, resized to 1024x960px, was originally 202KB. After optimization, it's just 57KB.
TinyPNG is free to use if you're optimizing up to 500 images per month, which is plenty for most bloggers. As with most API services, you need an API key to use TinyPNG (the workflow has an import question that prompts for this).
Before you start optimizing images, keep in mind that TinyPNG is a web service and you're uploading images to a third-party. It's entirely up to you about what images you feel comfortable optimizing. I'm happy to use this for any public images and screenshots I'd share on my blog anyway, though I wouldn't use it to optimize images that contain sensitive information (scans of passports, screenshots of bank account details, etc.).