1) Find this part in the plugin file and set these values:

		$ras_angle = 2; // Degrees to tilt the text
		$ras_offset = 5; // Pixels to offset the text from the border
		$ras_fontsize = 16; // Default font size for the anti-spam image

2) Find this part in the plugin file and set this value (the "6"):

		// if the text height too big for the image, decrease the font size to a certain extent (best practice is of course not to use really long words!
		while ($ras_boxheight > $ras_imgheight - $ras_offset && $ras_fontsize > 6) {

3) Rearrange this:

antispamdiv.innerHTML = '<p><input type=\"text\" name=\"securitycode\" id=\"securitycode\" size=\"30\" tabindex=\"4\" /><input type=\"hidden\" name=\"matchthis\" value=\"' + randomtext + '\" /><a href=\"#regenantispam\" onclick=\"RegenAntiSpam();\"><img src=\"" . $ras_myurl . "?antiselect=' + randomtext + '\" alt=\"Anti-Spam Image\" style=\"border:1px solid " . $ras_borderclr . "; vertical-align:top; height:" . $ras_imgheight . "; width:" . $ras_imgwidth . ";\" /></a></p>';

to this:

antispamdiv.innerHTML = '<p><a href=\"#regenantispam\" onclick=\"RegenAntiSpam();\"><img src=\"" . $ras_myurl . "?antiselect=' + randomtext + '\" alt=\"Anti-Spam Image\" style=\"border:1px solid " . $ras_borderclr . "; vertical-align:top; height:" . $ras_imgheight . "; width:" . $ras_imgwidth . ";\" /></a><input type=\"hidden\" name=\"matchthis\" value=\"' + randomtext + '\" /><input type=\"text\" name=\"securitycode\" id=\"securitycode\" size=\"30\" tabindex=\"4\" /></p>';


4) Rearrange this:

			echo( '<div id="randomantispam"><p><input type="text" name="securitycode" id="securitycode" size="30" tabindex="4" />'."\n\t\t\t\t" );
			echo( '<input type="hidden" name="matchthis" value="' . $ras_antiselect . "\" />\n\t\t\t\t" );
			echo( '<a href="#regenantispam" onclick="RegenAntiSpam();"><img src="' . $ras_myurl . '?antiselect=' . $ras_antiselect . "\"\n\t\t\t\t" );
			echo( 'alt="Anti-Spam Image" ' );
			echo( 'style="border:1px solid ' . $ras_borderclr . ';vertical-align:top;' );
			echo( 'height:' . $ras_imgheight .';width:' . $ras_imgwidth . ";\" /></p></div>\n\t\t\t" );
			echo( "</div>\n\t\t\t" );

to this: 
			echo( '<div id="randomantispam"><p>'."\n\t\t\t\t" );
			echo( '<a href="#regenantispam" onclick="RegenAntiSpam();"><img src="' . $ras_myurl . '?antiselect=' . $ras_antiselect . "\"\n\t\t\t\t" );
			echo( 'alt="Anti-Spam Image" ' );
			echo( 'style="border:1px solid ' . $ras_borderclr . ';vertical-align:top;' );
			echo( 'height:' . $ras_imgheight .';width:' . $ras_imgwidth . ";\" />");
			echo( '<input type="hidden" name="matchthis" value="' . $ras_antiselect . "\" />\n\t\t\t\t" );
			echo( '<input type="text" name="securitycode" id="securitycode" size="30" tabindex="4" /></p></div>' . "\n\t\t\t" );
			echo( "</div>\n\t\t\t" );