This is quite tricky because the sample image has 24 different projections, one for each UTM zone.
To get this right, the best way is to find a grid of UTM lines (eg from the world database on the install disks datasets when it was included with the software)
Then clip each zone out and register it with the correct zone set for a reference grid.
Rectify the strip image making sure that the projection is defined.
Reproject the image to another projection, say mercator and merge the strips back.
If you have 26 that is 26*24 or 625 registrations by hand so it needs automating.
If you can, make each image identical by clipping exactly the same so they stack up exactly.
Then create a set of control points, six for each strip on the top combined sheet and save.
Use the control points clip, register and reproject the set. Still a lot of scripting, sorry.