If you are compiling a WinHelp project then there are only three possible image alignments, left, centered in text and right.
If you are compiling for HtmlHelp then you have more control. Double-click your image and the "Image Properties" screen appears.
You can experiment with the best alignment for your needs. However the changes will only be shown when you compile. Fast-Help deliberately sets the visual alignment within the editor to "centered in text". This is because the performance overhead of redrawing the screen every time a character is typed in, to create the correct wrapping, is too great. So a compromise of performance and visual aesthetics was made within the editor.