I just downloaded ActivePerl, installed the MinGW package using PPM (which also installed dmake), and successfully built Imager.
I see you're using g++ but yet using nmake - typically if you're building perl or perl modules using the GNU toolset on Windows, you need to use dmake as the make tool. If you installed MinGW using ppm it should have also installed dmake.
As to the jpeg issues, please let me know where you got the jpeg libraries and headers you're using - you can't just copy a libjpeg DLL and expect Imager to build JPEG support from that, Imager needs to find the headers and link libraries at Makefile.PL and make time.
When you run Makefile.PL you'll see a summary like:
done.
gif: includes found - libraries found
ungif: includes found - libraries found
jpeg: includes found - libraries found
png: configured via `pkg-config libpng ...`
tiff: includes found - libraries found
freetype2: configured via freetype-config
T1-fonts: includes found - libraries found
TT-fonts: includes found - libraries found
If the jpeg line reads like the above, then Makefile.PL found what it needs, if it reads like:
Then you're either missing libraries/headers, or you need to tell Makefile.PL where to find them.
To add to the include search path, supply a --incpath option, eg --incpath=c:\some\path
To add to the library search path, supply a --libpath option, eg --libpath=c:\some\path
Please let me know how you go with this.
Tony