I can't be sure, but I think you could use a shortcode.
It has been a LONG time since I worked with Excel macros, so bear with me. I assume that you can separate 2 comma separated values in a cell into the 2 parts.
What I am suggesting is that you put the comma separated values for the title/alt and the relative path to the image, something like this, in the Excel column: Nice Day,sun.jpg
Excel would generate: [post_img img="sun.jpg" alt="nice day"]
Then you would code a function (in functions.php) to process the post_img shortcode and return this:
<a href="http://mysite.com/this-page" title="nice day"><img class="alignleft" src="http://mysite.com/content/uploads/sun.jpg" alt="nice day" title="nice day"></a>
The href can be obtained using the get_permalink() function.
The uploads path can be obtained using the wp_upload_dir() function.
Here is a Codex article on using shortcodes: