I have been tasked to create a list of point symbols for the counties Watershed Improvement Program from scratch. They don't want modified icons from the programs database, but custom drawn. I already have the hand sketched symbols approved and I'm using Inkscape to create the vectors. Now to the actual question: Is there a step-by-step process from converting the .bmp or .png files to Esri symbols? Ie. what size and format should the vector be created in, how do you upload into Arcmap (10.1), and how do you access your folder in the Style Manager? I know this may seem simple to a lot of you, but the Googled help I've seen is about as simple as Greek Calculus to me.
For sizing. It looks like some of the .bmp examples are set up as 16x16. If you look at your folder :\Program Files\ArcGIS\Desktop10.1\Styles\Pictures you can see the other examples of pictures that ESRI uses in ArcMap. You can style your photos similar to that size wise and quality wise.
Now that you have an image.... In ArcMap, go into the Symbol Selector for the layer you wish to use the layer for (click on the symbol in the Table of Contents as a shortcut). In there, click on Edit Symbol. Since you're using point symbols, you will see Type saying something like Simple Marker Symbol in the drop down while you're in the Symbol Property Editor screen. Hit that drop down and select Picture Marker Symbol. Navigate to your picture and select it.
This will add in your photo to play with and see how it looks. From there, you can see how to add custom photos and such into your display.
Update: For making your own style.... If you go to Customize under your menu bar, you can access the Style Manager to customize it. You can save your photos into an existing style or create a new one. If you follow the steps in the first help link I posted underneath, it is pretty self-explanatory.
Either method would work to get your symbols on the map, but if you generate a new style, you don't have to go through the hassle of adding pictures individually every time.