1) Application.CurrentProject.Path will return the folder that the db is in. If you standardize the image folder (e.g. C:\Databases\YourApplication\Images) and the db is in the same root (e.g. C:\Databases\YourApplication) then about all you'd need to do is concatenate the left part & \ & the standard path to the images folder.
2) if this is a one time thing, just use File Explorer and be done with it. Going forward, use the file dialog object as you suggest, but start where the path is equal to the concatenation you will already have or can build when the fd is invoked.
The more we hear silence, the more we begin to think about our value in this universe.
Paraphrase of Professor Brian Cox.