How can I reset the camera roll to photo IMG_0001.jpg on iOS?
With an Application such as iExplorer navigate to PhotoData / MISC where you'll find a file called DCIM_APPLE.plist which contains the following:

&lt;plist version="1.0"&gt;
&lt;dict&gt;
    &lt;key&gt;DCIMLastDirectoryNumber&lt;/key&gt;
    &lt;integer&gt;100&lt;/integer&gt;
    &lt;key&gt;DCIMLastFileNumber&lt;/key&gt;
    &lt;integer&gt;251&lt;/integer&gt;
&lt;/dict&gt;
&lt;/plist&gt;


The DCIMLastFileNumber parameter is quite self explanatory. Set the number at which you want the counter to start at and restart the iPhone to apply the changes.