Let us step back to the original request about how to insert a picture within a post so that, when clicked, it will take the viewer to a larger version of the same picture, hence allowing more detailed examination.
The only caveat I would add here is that you should try and keep your original pic to a reasonable size, say 800 pixels wide, so that people with slower dial-up connections don't have to wait an age for them to be downloaded to their screen. The real down-side to making the pictures 'huge' is that people might stop visiting if they feel that they have to wait an unnecessarily long time for something to display!

These are views of my garden when I was lucky enough to live in Cyprus for a short time. The house and garden were perched on top of a cliff that overlooked the blue Mediterranean. Glorious!

I just uploaded the originals to Blogger, chose to have them display as 'centred' and in a 'medium' format (size) on the page, and Blogger did the rest.
Now that Blogger had done the hard work I then clicked on the 'edit' icon below the post and chose to edit the HTML version, but only to add a couple of little 'extras'.

You should make it a rule for any picture you display on your site to 'identify' it by giving it some 'alt' text. This helps the visually impaired who may be using a screen reader to access your blog. I did this in the code that Blogger generated. The second thing I did was to insert target="_blank" at the end of the code line so that when a viewer clicks on the picture it is opened in a new window. Frowned on by the W3C standards validation people, but I will explain my reasons at a later date!
Nothing difficult about that, huh?