Suggestion from Julian that the Grid format should provide a way of allowing the user to set the size of the image and its containing box through course settings in the same way that Collapsed Topics does with it's settings.

I consider that this should be implemented in 2.5 as would not require a new database table and custom form.

NOTE: The requirements below are now 99% finished. If you have any comments to make then please do so by 10th October 2013 or sooner.

Requirements:

1. Ability to set the width of the image container (icon) as a x in pixels and have the height calculated by a ratio. Widths of: 128, 192, 210, 256, 320, 384, 448, 512, 576, 640, 704 and 768. Ratios of: 3-2, 3-1, 3-3, 2-3, 1-3, 4-3 and 3-4.
2. When uploading the maximum width size setting shall be applied to the image to avoid large file sizes in storage / downloading bandwidth.
3. As a consequence of 1, up scaling the size of old courses will result in pixelation, therefore the user should re-upload an original copy of the image.
4. Ability to change the border colour, radius (same as width and on / off setting) and width. Widths of: 1 - 10.
5. Ability to change the image container (icon) background colour.
6. Ability to change the current selected section colour with defaults.
7. Ability to change the current selected image container (icon) colour with defaults.
8. Width and ratio settings to be editable on the course settings form and stored in the config_plugin's table using existing 2.5+ core code.
9. Default width, ratio, border colour, border radius on /off, border width, image container (icon) background colour settings to be made available to be set by the site administrator in 'Plugins -> Course formats'. Values to be transposed from current CSS style.
10. Ability to reset to default the settings for the course in the 'Edit settings' of the course.
11. Ability for the site administrator to reset to default the settings for all grid format courses.
12. Ability for the site administrator to prevent setting changes through the implementation of custom capabilities in 'db/access.php' and checks in 'lib.php'. Two capabilities 'changeimagecontainersize' and 'changeimagecontainerstyle'.

Proposal video: http://www.youtube.com/watch?v=G1zHTEdfP9o