The simplest way to create the blog image is create a canvas of blog image size and select a background for the blog and then place the content in the image your blog image is ready, but if you want to create a good looking blog image then you should do some more efforts in making the blog images. Now i am telling you some design patterns which you can use and implement in your blog images, create a canvas of blog image size in which you have to share or post the blog, you can use the pattern like divide the screen into two parts one side is for image and other side is for content you can do one thing also place a solid background under the content area so that your content should be visible properly.
Another pattern is take a background place it in the canvas and then take a solid color rectangle after that decrease the opacity of the rectangle until the image is visible only 20% so now your background is ready, next step is to place a content in the blog image write the text in the middle of the image draw some kind of lines for the look and your blog image is ready. Another pattern is that you can create a canvas and after that place a background then you place content left side of the image or right side of the image but one difference is there is a strip under the content for the visibility purpose tripe should be dark shade, you can also create a background by cutting slantly of more than one images it looks nice in the background, you also can use graphics created by your own or download it from any site like the social media icon and other small icons that makes your blog image perfect.