Helpful comments by Colin Berry remind me that I need to mention Mario Latendresse’s absolutely fantastic Shroud Scope again. I last mentioned it in September of 2011. Here is some descriptive material from the help page (BTW it seems to work now with the latest release of Internet Explorer 9 (9.0.6) although performance seems much better with Chrome and with Firefox):
The Shroud Scope has been successfully tested on the following browsers: Firefox, Chrome, Safari. Sorry, the Shroud Scope currently does not work on Internet Explorer (IE).
This Web page describes the functionality of the Shroud Scope, a Web interface to display high definition photographs of the Shroud of Turin, zoom-in and -out these photographs, activate overlays and do length measurements over them.
The Shroud Scope has currently two different photographs: the 1931 Enrie photograph (shown in negative) and the 2002 Durante photograph (shown in positive). Both photographs have two versions: vertical and horizontal. At the highest zoom-in level, the Durante photograph offers a resolution of 0.17 mm per pixel (a pixel is a dot on your screen). As far as we know, this is the highest resolution photograph of the Turin Shroud publicly available on the Web.
The initial Shroud Scope Web page contains several widgets, panels, and icons as seen on the following screen snapshot.
In the following paragraphs we give brief descriptions of them but more details are available in the subsections below.
The Switch Panel widget is the blue panel that appears on the right side, near the top, of the Web page. If it is closed, click the plus icon to open it. It displays two lists: Base Layer and Overlays. The list of base layers is above the list of overlays. Each base layer is a photograph of the Shroud of Turin. Only one base layer can be active at a time whereas several overlays can be active at the same time. Select the desired base layer and overlays by clicking their title or their radio button in the Switch Panel.
The Ladder widget is the blue widget in the form of a ladder with over 10 steps displayed on the left of the Web page. It is used for zooming-in and -out the current active photograph (aka base layer). You can click on any ladder step to go directly to a specific zoom level. You can also use the plus icon to zoom-in or the minus icon to zoom-out. The first zoom level, the lowest, displays a 3%-scale image of the original image used at the highest zoom level. It is very small and should fit almost any computer monitor size. The second zoom level displays a 5%-scale version, the third zoom level is a 10%-scale version, the fourth zoom level is a 20%-scale version, and so on by increment of 10% up to the highest zoom level at 100%. At that zoom-level, it is the highest definition that can be displayed.
The colorful rounded-square icons on the right of the Web page can be used to activate different tools. There are three tools: panning, measure, and permalink. These tools are described on this Web page below. To activate a tool icon, simply click it. An active icon that has a reddish hue means that it is active and that the state of the Shroud Scope has changed. For example, if the measure tool is active, no panning can be done, and vice versa. A tool remains active until you click another tool. When you first visit the Shroud Scope Web page, the panning icon is active. The panning icon enables you to move (or pan) the entire photograph on the Web page.
The Base Layers
A base layer is essentially the main Shroud photograph shown on the Web page. Currently, two images are available, displayed horizontally or vertically, that is four base layers are provided: Enrie Negative Horizontal, Enrie Negative Vertical, Durante 2002 Horizontal, and Durante 2002 Vertical. More base layers are planned for the future. The Durante 2002 photograph has the highest definition. As far as we know, this is the highest definition photograph available on the Web, worldwide. (emphasis mine)
And BTW, take some time to browse the entire site at www.Sindonology.org. There is some excellent material there.