problem with VGA display of a static image

It does sound like the pixel data is arriving at the VGA output ok. There are a few things that I can think of that may be going wrong.

1. The ROM has an old .mif file stored in the Quartus db folder. You can either select "Update memory initialization files" from the processing menu or delete the db folder.

2. The ROM .mif has an incorrectly formatted image. (colors can be wrong, picture resolution may be different) Try writing a basic process that outputs a black screen for half of the image and a white screen for the other half. (do this twice - top/bottom and left/right) This will ensure that you are outputting the video format you expect. (if your image rolls or isn't half of your display, your assumptions on the horizontal and vertical sizes are probably off)

The dual port ram should work if your addressing is good. It is one way to cross the clock domain from 50MHz to 25MHz. That's about as much help as I can give you for now. Try (1) first. It is easier and faster to test than (2). Good luck!