Think about Image Optimization, That will help you to speed up your site.
Reduce image file size
This is important to increase Google Page Speed score.
Yes, I'm going to say about your images which are waiting to get your permission to upload themselves on your site. We believe that big and high- res images are better for user experience, But often they have a very large file size and take a long time to load your site or page. So, take images in Kb not Mb. It can be between 100kb to 500kb in large.
As a designer when I'm using Photoshop to edit or optimize images for web then I don't care about PPI or DPI, Because they are not necessary to web displays, but they are important for printings. Check below 2 images are saved with different dpi, but you won't see any gap between them in quality.
|800 x 534 at 300dpi|
Photo Credits : Clipping Path Specialist
|800 x 534 at 72dpi|
Above both image file size that are the same 177kb, Respectively. There isn't any impact in file size by increasing or reducing the dpi. When we need to make our image under 500kb then think on it's dimensions (width and height of image). Because an image at 800 x 534 contains 427200 pixels, That's what determines the file size. So, a larger image contains more pixels, As a result file is larger.
However, when you are using Photoshop to prepare your images, you should aware on width-height and choose "Save for Web" to save it.
If you are not familiar with Photoshop, you can compress your images to get a smaller file size by some online tools, such as Compress JPG , Tiny PNG , Compressor io and so on.