Images, as well as text, should be adapted to the place of publication using tools designed to process images such as popular:
The images you publish on the website using the CMS system should be optimized and be in JPG format. The JPG format works in 100% browsers and is therefore the best choice. In addition to the JPG format, PNG is also used for the raster image format, raster images are "artificial", digitally generated graphics.
There are some other formats such as webp but they do not have 100% support so you still need to set up a jpg / png alternative so that all users have a good experience. When it comes to extremely highly visited sites it makes sense to deal with the webp format otherwise there are smarter things to spend time and money on.
Often clients want to process their photos using the CMS system, but this is not possible and if possible it is limited to basic actions such as resize, optimize ... This is a fact that needs to be reconciled and cannot and should not be forced beyond applications that are already listed above.
The image resolution, in 99% of cases, should not exceed 2560px and in most cases it is advisable to choose a lower resolution such as 1200px because it is often sufficient and covers the most commonly used width of the website.
The best aspect ratio for the website is 4: 3 and for banners is 3: 1, with the proviso that this ratio does not work well on mobile versions of the website, so it is often supplemented with a 1: 1 ratio, but the 4: 3 ratio also works great.
Each jpg image is compressed according to a certain quality that has a scale from 1% to 100%. For the web it is best to use values between 60% and 80% depending on the need, it is difficult to define the exact number because all photos are different and are subject to the subjective impression, the perception of the observer.
As a rule, 90% of photos should be smaller than 1MB and range from 200KB - 800KB depending on the details, the complexity of the photo.
The multimedia of each website has the greatest impact on the speed of the page itself and takes up a minimum of 75% of the space stored on the server, so it is important to have a clear plan from the beginning on how to deal with photos. The processing and preparation process cannot be skipped and there is no magic automatic tool that will do the job for you.