- Original size is not usually a good option, unless you are maybe using a smaller image. You never want to make an image bigger than it's original dimentions because the it will become pixelated.
- XL is 640px on the long edge and fine for most blogs, but photo blogs it can be a little small in these days of large screens!
- L (400px), M (320px ) and S (200px ) are not really very useful, but do I occasionally use them if I want to put images side by side.
The first challenge is to find the image you want to resize! It's actually easier if you are doing them all because you can use this trick: press Ctrl+F on your keyboard and in the top right hand corner of your screen a little box will appear. Punch in 1024 and every instance of that search will be highlighted in the your post (btw - you can use this on any web page when searching for something ~ VERY useful!)
NB~ if you have used Option One to import your images via the url, you may find Blogger has auto-resized them and made them all smaller. In which case you need to search and replace the number 320 instead of 1024.
The pictures below shows you the code for a single image (it looks a tiny bit different depending on which method you used to import your image to Blogger). You might not be able read my notes in red on the first picture, but essentially you need to replace the number 1024 with either 920 if the image is landscape, or 720 if it's portrait. These are standard blog sizes, but you can actually choose any size you like these days!
( I find 920 width is a good compromise of large size and reasonable loading speed. And I choose 720 height as ideal because the pictures fit most screens without needing to scroll! Many people use 800 for both width and height ~ it's really up to you! )
Once you have changed the 1024 number you then need to completely obliterate the other measurement! (As I have shown on the first image - delete all the code I have put a line through)