The article contains several bits of information that will be useful:
Extensive fields of large fractured plate-like features on a horizontal surface are visible near the south end of the High Resolution Stereo Camera (HRSC) imaging strip taken on 19 January 2004 (Fig. 1). This area has previously been covered by NASA high-resolution Mars Orbiter Camera (MOC) imagery at pixel sizes down to 1.8 m (Fig. 2).
Part of an HRSC image of Mars from orbit 32, with a resolution of 13.7 m per pixel, centred at 5.5° north latitude and 150.4° east longitude, showing plate-like deposits with signs of break-up, rotation and lateral movement to the west-southwest in the lower part of the image.
High-resolution MOC images E2100112 and R0900475 of an impact crater seen in Fig. 1a.
We infer that the evidence is consistent with a frozen body of water, with surface pack-ice, around 5º north latitude and 150º east longitude in southern Elysium.
The data from Mars Express is archived here. The ESA Planetary Science Archive has a more searchable archive, where you can find images by date and by instrument. That yields a list of images that might be useful as a starting point. I expect the image metadata will contain the map coordinates of each image.
I downloaded one of the HSRC images (120 MB). In the IMG file, there is a bunch of metadata. You can open the IMG file with a text editor to see them.
FOOTPRINT_POINT_LATITUDE and FOOTPRINT_POINT_LONGITUDE are what you need, but instead of a single long/lat pair you get a series like
It looks like this is a strip image of a very large area. So you'll need some more information to map that to the areas in the image.
The MOC images are probably an easier way in, as they cover a smaller area than the HSRC images. So, go to the NASA PDS, enter MOC E2100112 in the search field and the image turns up. No lat/long in the image label, though.
Or you can email the author. His mail address is in this PDF.