Google requires the webpage to load in less than a few seconds to give you a first page rank in the search results. Therefore, you need a tool to optimize the size of the image before inserting the illustration into WordPress.
TinyPNG, EWWW Image Optimizer, and Kraken.io go head-to-head. The results depend more on what your needs are (as always!).
For years now, WP Smush has been the most popular free image compression plugin for WordPress with more than 200,000 active installs.