The resource links I have are these ones:
http://wpbtips.wordpress.com/2010/05/01/introduction-to-structure/
http://wpbtips.wordpress.com/2011/10/21/on-the-recent-featured-image-issues/

For Structure:
640×392 pixels if you’re using the option to display the featured image when viewing a single post.
620×380 pixels if you’re not using that option.
(620×380 is the size of the homepage top featured image, 640×392 is the size on the single post view; but 620×380 and 640×392 are the same aspect ratio, so the image will show up in the homepage top area in both cases).
featured images > http://en.support.wordpress.com/featured-images/
Setting a Featured Image > http://en.support.wordpress.com/featured-images/#setting-a-featured-image

So I've been using the structure theme which should show featured images on my main page (and did so perfectly on an old blog I used to manage!) but for some reason it's refusing to show any of them apart from the featured image on my very first post. I've been doing what always worked before (i.e. to make an image show up setting the image I want as the featured image for the post and et the theme options to feature images in the order published rather than by category) but to no avail - any advice?

When you insert an image, that blog will remember which selection you used previously. One of your blogs brings you to an attachment page (post url), the other to the file url. Just choose whichever option you want for whichever blog you like. The choice should be "remembered" in future.

See here for more detail:
http://wpbtips.wordpress.com/2009/04/26/images-the-three-link-options/

I'm using the theme 'Fresh and Clean' for two different blogs. On the first blog http://www.disneypincollecting.wordpress.com, when you click an image it takes you to a page that has the image caption and retains the header, main menu, etc. On my second blog http://www.disneymemories.wordpress.com, however, when you click an image it takes you to just the image on a blank background.

I KNOW there is a way to fix this! I remember there was an option when I was working on my first site but now I can't find it. Help!

Anyone with expertise using the Fresh and Clean theme please let me know!

Cheers!

Second thing, you can not do this with PHP. You can do this with ASP.Net...
You can use this Plugin if you wish:
http://wordpress.org/extend/plugins/dynamic-content-gallery-plugin/

I'm using my own custom design template, and wish to embed some images into the design. Some of these images are static, and are simply stored in the template's /image directory. Some of these images however are dynamic and I will wish to change them every now and then. For simplicity, I would like to upload these dynamic images into my Media Library and then simply display them with the relevant function calls in my template code.

However, I cannot find how to do this. I've uploaded the images to the Media Library, but cannot find any php calls to fetch images from it. Do any such calls exist? If not, what is the procedure for fetching images from the library? Are there are any plug-ins available to do the job for me?

Many thanks.