svn:ignore

$  svn status Tracking

?       Tracking/ReadHits.C
?       Tracking/Run8090.R2.Wire17-23missing.png
?       Tracking/R2.Plane3.Wire17-23.png
?       Tracking/8090_r2_p12_allplanes.png
?       Tracking/R2.Plane3.Wire17-23.zoom.png

$ svn propedit svn:ignore Tracking

[] editor is opened, add

*.png

$  svn status Tracking

 M      Tracking
?       Tracking/ReadHits.C

Reference http://www.linuxtopia.org/online_books/programming_tool_guides/version_control_with_subversion/svn.advanced.props_5.html#svn.advanced.props.special.ignore