A .chm file can include only files that are located in the same directory as the .hhp file, or in a subdirectory of that directory. If your graphics files are located elsewhere, they must be copied to the .hhp directory or subdirectory. DITA2Go can do this for you.
To tell DITA2Go to fetch your referenced graphics:
[Automation]
WrapAndShip = Yes
CopyOriginalGraphics = Yes
When CopyOriginalGraphics=Yes, DITA2Go follows the file paths in your DITA source to find the graphics files to copy.
To tell DITA2Go where to put copies of the graphics (for example):
[Graphics]
GraphPath = ./graphics
The path you specify for GraphPath should be relative to the wrap directory (see §44.3 Understanding path values for deliverables). This path will be used in HTML output, as the relative path from the HTML files to their referenced graphics. If you use backslashes in the path, DITA2Go converts them to forward slashes before inserting the references in your HTML output. If you specify CopyOriginalGraphics=Yes, DITA2Go copies graphics files to the directory specified by GraphPath, after generating HTML files.
§18.13 Compiling and testing HTML Help