Image optimization
Be sure that the images on your website are optimized for web delivery. Photos directly from your phone are going to be too large (in terms of file size) to display on a website (it can be done, but it shouldn’t be).
If the file sizes are too large, you risk running into issues with load time, and this can be an issue for people in rural settings or on mobile phones.
It is also being implemented as a mobile ranking signal (that means it impacts your search engine rankings).
Ideally, photos on your website should be around 40kb in file size.
Photoshop
To optimize an image to get the file size down, you can use Adobe Photoshop’s “save for web” export feature to adjust the quality of the image to try to get the file size down. When you have the image open in Photoshop, go to File > Export > Save for Web, and a new export window will open. In the top right there is a Quality setting, and you can adjust this smaller to make the file size smaller. The file size shows in the bottom right of that same screen, also highlighted yellow. You can adjust the quality until you get the file size smaller. The image adjusts to show how the quality setting impacts the image — you don’t want to have the image too pixelated, so keep an eye on how the image is looking. At 1800px, you should be able to get the file size under 100kb and still have an image that isn’t pixelated.
TinyJPG
If you don’t have Photoshop, you can try this free online tool called TinyJPG: https://tinyjpg.com You can upload your .png or .jpg files and compress them right in a browser window.
In terms of file formats, photographs are usually best saved in JPG format, and graphics with flat areas of color are best as PNG or GIF. You can achieve transparent backgrounds with PNG or GIF.