I would like to know if there is any way to change the size of the image on the USS login page since I see that by default it only accepts images with 490x50 resolution.
You need to use equal height and width according to the product documentation.
See this thread for discussion and a link to the doco here:
Modify Report an Issue and Request a Service
Here's some comments, that although for an older release SDM 12.6, and not USS, probably have validity:
12.6 Changing Banner Image Size
And you can go here to vote on a related Idea to allow customisation in this area:
Enable customization on USS
In the meantime, the best workaround is to make your image fit, and then fill in "bits left over" with an appropriate background colour.
Retrieving data ...