１．MT/tmpl/cms/upload_complete.tmpl（135行目付近）　　［checkboxで検索した］

<p> <label><input type="checkbox" name="constrain" value="1" checked="checked"> <MT_TRANS phrase="Constrain proportions"> </p>

の部分の下に下記を追加

<p> Image floating:<select name="ifloat" class="menu" >
<option value="left" selected>left
<option value="right">right
<option value="none">none
</select>
</p>

そして同じく最後の方の

<div>
<TMPL_IF NAME=IS_IMAGE>
<input type="button" onclick="doClick(this.form, 'popup=1&width=<TMPL_VAR NAME=WIDTH>&height=<TMPL_VAR NAME=HEIGHT>&image_type=<TMPL_VAR NAME=IMAGE_TYPE>')" value="<MT_TRANS phrase="Popup Image">" />
<input type="button" onclick="doClick(this.form, 'include=1&width=<TMPL_VAR NAME=WIDTH>&height=<TMPL_VAR NAME=HEIGHT>&image_type=<TMPL_VAR NAME=IMAGE_TYPE>')" value="<MT_TRANS phrase="Embedded Image">" />
<TMPL_ELSE>
<input type="button" onclick="doClick(this.form, 'link=1')" value="<MT_TRANS phrase="Link">" />
</TMPL_IF>
</div>

<div>
<TMPL_IF NAME=IS_IMAGE>
<input type="button" onclick="doClick(this.form, 'imgfloat='+this.form.ifloat.value+'&popup=1&width=<TMPL_VAR NAME=WIDTH>&height=<TMPL_VAR NAME=HEIGHT>&image_type=<TMPL_VAR NAME=IMAGE_TYPE>')" value="<MT_TRANS phrase="Popup Image">" />
<input type="button" onclick="doClick(this.form, 'imgfloat='+this.form.ifloat.value+'&include=1&width=<TMPL_VAR NAME=WIDTH>&height=<TMPL_VAR NAME=HEIGHT>&image_type=<TMPL_VAR NAME=IMAGE_TYPE>')" value="<MT_TRANS phrase="Embedded Image">" />
<TMPL_ELSE>
<input type="button" onclick="doClick(this.form, 'link=1')" value="<MT_TRANS phrase="Link">" />
</TMPL_IF>
</div>

２．MT/lib/MT/App/CMS.pm （1889行目付近）　［'popup_image'で検索］

if ($q->param('popup')) {
require MT::Template;
if (my $tmpl = MT::Template->load({ blog_id => $blog_id,
type => 'popup_image' })) {
(my $base = $q->param('fname')) =~ s!\.[^.]*$!!;
if ($base =~ m!\.\.|\0|\|!) {
return $app->error($app->translate(

この部分の前に以下を挿入

my $imgclass;
if ($q->param('imgfloat') eq 'left') {
$imgclass = " class='l' ";
}elsif ($q->param('imgfloat') eq 'right') {
$imgclass = " class='r' ";
}else {
$imgclass = '';
}

そして1931行目付近

my $link = $thumb ? qq(<img src="$thumb" width="$thumb_width" height="$thumb_height" border="0" />) : "View image";
return <<HTML;
<a href="$url" onclick="window.open('$url','popup','width=$width,height=$height,scrollbars=no,resizable=no,toolbar=no,directories=no,location=no,menubar=no,status=no,left=0,top=0'); return false">$link</a>
HTML
} elsif ($q->param('include')) {
(my $fname = $url) =~ s!^.*/!!;
if ($thumb) {
return <<HTML;
<a href="$url"><img alt="$fname" src="$thumb" width="$thumb_width" height="$thumb_height" /></a>
HTML
} else {
return <<HTML;

<img ○ alt="$fname"

３．最後にstyles.css テンプレートに、以下を追加

img.r {
float: right;
border: none;
margin-right:4px;
margin-top:4px;
vertical-align:top;
}
img.l {
float: left;
border: none;
margin-right:4px;
margin-top:4px;
vertical-align:top;
}

おしまい＾￥＾