Make your images Enchanced Metafile Format (.emf)

The Windows Enhanced Metafile (EMF) is the best format for inserting images as pictures in ArcMap. EMF files allow resizing of images in ArcMap without the loss if integrity or resolution, which you may see if you use a JPEG or BMP formatted image.

http://gis.sfsu.edu/helpdesk/arcmap/layout.htm

You would think ESRI would support IMPORT of .svg but sadly no ONLY export.

Make your images Enhanced Metafile Format (.emf)

The Windows Enhanced Metafile (EMF) is the best format for inserting images as pictures in ArcMap. EMF files allow resizing of images in ArcMap without the loss if integrity or resolution, which you may see if you use a JPEG or BMP formatted image.

http://gis.sfsu.edu/helpdesk/arcmap/layout.htm

You would think ESRI would support IMPORT of .svg but sadly no ONLY export.