Using quartus megawizard create a rom mega function. Depending upon the size of your image you could choose to implement the rom using the internal block RAM or distributed RAM. As part of the ROM mega function creation, you will have the opportunity to create a MIF ( memory initialization file.)
Create a mif file from your txt file and specify that file as initialization file for your ROM.
E.g. method to create mif from txt is described here - http://www.alteraforum.com/forum/showthread.php?t=27934