RoboHelp just dumps it in the root, unfortunately. The easiest way is to first place your images in the folder you want to have them and then include them in your topic. If you can create a macro to do that for you, then Bob's your uncle.
The solution I have for cleaning up is a script to move all those images to the same folder as the topics they are used on. (Note: paid script.) See: HelpEssentials » Image Mover
If you paste images into your topic, RoboHelp names them in numerical sequence, based upon the names of the images already in the target folder. To then drag the images in Project Manager you have the issue of files in the target folder having the same name as what was just created. If you could specify at least an "images" folder instead of the root project folder, it would be much cleaner organization and would avoid the duplicate name issue.
Yes, you can always insert your image by browsing to the image file and then it will have whatever name you have already given it and this avoids the duplicate name problem. However, this is not always the most expedient (or necessary) way to insert graphics and it still doesn't resolve the problem of the default image folder for the project.
Looking at it from a developer's perspective, how would you want them to name the files. In the absence of users naming a file the apps I have encountered use numbering. I guess they could use "overall" numbering but that would mean look at the highest number in use, with a time hit.
Best thing here is for you to suggest what you would like in a feature request. Please follow this link. You can use the link to request new features.
Perhaps post your thoughts here first to get input from others.
See www.grainge.org for RoboHelp and Authoring information
There is no issue with how they name the files. It only becomes an issue when we have to manually move the image files to the desired folder, and then later add new images which will, again, need to be moved to the desired folder. At that point there is a conflict of duplicate names. The problem then, is that we cannot specify a default image folder. If we could do that, there would be no reason to manually move the files and the current naming process would be fine. (Not to mention that is much easier than coming up with a new way to name the files, though both could be solved with a dialog - with a "do not ask again" - when the image is pasted which allows for name/path changes. But I digress.)
Manually moving image files is not a solution; it is a workaround. The problem with workarounds is that they are not as efficient as actual solutions, and there are often other issues which arise (requiring their own workaround processes) due to the fact that the program itself can't be designed to predict random user workarounds.
Robohelp actually places a lot of files in the project root directory. I understand ... it has always been this way and no one has revisited how this is done. The only files that should reside in the root by default would be the topic files (and having a folder structure for these and adding new topics to folders is easy as pie, so that part is already user configurable). No configuration files or js or css ir index or TOC etc. should be in the root. It's just sloppy organization. Back when all this stuff was new, the fact that we could create a system like this at all was very cool. But now we have more knowledge and experience under our belts; we are hopefully wiser and our standards much higher.
But one thing at a time. Starting with the ability to specify a default folder for images.
I did add this as a feature request using the link you provided.