It's always important to avoid duplicate filenames for your graphics because of the way Help+Manual manages graphics and locates your graphics files. This applies in particular for modular projects, because you will often have separate graphics folders for each project.
Duplicate names are OK if you use runtime merging because then each module is published individually and the correct graphics will be used. However, if you use publish time merging Help+Manual will only find the first instance of any duplicates as it searches through the graphics folders to locate the correct files.
•The simplest solution for this problem is to add a unique prefix to the filenames of graphics files used in modules, in the same way that you use prefixes for the topic IDs in modules.
•The prefix should be short – two letters and an underline character are usually plenty – and should identify the module.