The original image appears to be protected from download - I agree with the other poster that you would need access to the original Scene7 server management software, and the passwords with which each image server is most likely protected. But that doesn't stop you sending legitimate http requests to the image server.
You'll probably have already worked out that changing the numbers in the ?wid=890&hei=550 part of a scene7 image link changes the size of the image you get back.
However if you substitute that with ?scl=1 then you will get the image in the same resolution (I believe) as the master image stored on the site, subject to some restrictions - as the previous answer points out many scene7 servers are limited to 2000x2000 pixels (You'll get an "illegal image size" message if so). Making the scale number greater than 1 makes the image smaller (e.g. 4 is 1/4 the size) and you can request larger than the original (0.5 etc) but not all servers allow this (and all you get is a blurry upscale anyway).
The way around this is to request the image as multiple tiles, using &rgn=0,0,2000,2000
The first two digits are the x and y positions (taken from the top left of the original) and the second two the image size, set to the maximum 2000x2000.
Gives the first and for the other three you need ?scl=1&rgn=0,2000,2000,2000, ?scl=1&rgn=2000,0,2000,2000 and ?scl=1&rgn=2000,2000,2000,2000.
You'll need to combine the tiles yourself in an image processing program - or if you have a huge screen resolution, write a simple html page and do a screen capture of all four tiles as one page. (You'll get white space where the original is smaller than the tile size, i.e. at the bottom and right hand side of the image).
Aside - Note the digits relate to the original image on the server, NOT what is returned, so with a scale of 4 and size of 4000, you'll get 4000/4 i.e. 1000 pixels - hence ?scl=4&rgn=0,0,4000,4000 doesn't cause an error.
Other useful commands are &resMode=sharp which processes the image server side to sharpen it (useful on smaller images), &fmt=jpeg which gives jpeg format (png generally also works, and on some servers tif) and &qlt=75 which forces the quality of the returned image (try 10 and 90 to see the effect). You can also combine commands e.g. ?scl=2&fmt=jpeg gives a jpeg image scaled to half the size of the master image.
e.g. a small png image focussing on the Nike logo:
As the another poster mentions, beware of copyright however - you don't own these images and without asking you don't have permission to use them. This is for education and information only!