Thing is, that's how the graphics were made in this game. There are a couple twists and tricks that could improve the game's graphics, however.
Read about the DosBox config file.
fullscreen=true
fulldouble=true
NOTE: Should improve the graphics, but increases the CPU load considerably.
fullfixed=true
fullresolution=[input the max resolution your screen can handle]
output=ddraw
NOTE: DirectDraw graphics output smoothens the image a bit
aspect=true
scaler=advinterp3x
NOTE: This is the best scaler if you want to improve the graphics quality.
That's about all that can be done here.