In Ubuntu 14.06, installing GDAL for development was straightforward if installed from the main repo (GDAL 1.9):
g++ `gdal-config --cflags` myProgram.cpp `gdal-config --libs` -o myProgram
Luckily, GDAL comes with a few off the shelf utilities. In particular, I found gdal_translate. This utility not only allows me to dump the .IMG file directly into a 16 bit grayscale PNG, but also it allows me to crop it so that I only get the useful info out of the file. Because one picture replaces a thousand words, this is what I mean. Below is an example of how I used the utility to create the PNG I ended up loading in UE4.
gdal_translate -scale 0 2560 0 65535 -srcwin 0 0 5355 3465 -ot Uint16 -of PNG testIMG.img testPng.png
Finally, this is a rendering of the result using a simple one layer landscape material (grassy), a bit of fog and a simple stationary directional light.