<asp:ContentPlaceHolder
id="PlaceHolderLeftActions"
runat ="server"/>
some times picture library thumbnail view wont work properly (for ex when you add it to site pages or any other pages). here is the small fix for this.
1) add content editor webpart to your page and select Content editor webpart the one you added and go to EditHtmlsource > copy and paste below code.
2)that's it.. now you are good to go....
<TABLE style="padding-top: 8px" cellSpacing=0 cellPadding=0 border=0 width=100%>
<TR valign=top><TD> </TD></TR>
</TABLE>
<TABLE id=ImgPreviewTable cellSpacing=2 cellPadding=0 border=0 width=100% style="display:none">
<TR><TD vAlign=center >
<SharePoint:EncodedLiteral ID="EncodedLiteral1" runat="server" text="<%$Resources:wss,piclib_picturePreview%>" EncodeMethod='HtmlEncode'/></TD></TR>
<TR><TD class="ms-navline" width=128><IMG SRC="/_layouts/images/blank.gif" width=1 height=1 alt=""></TD></TR>
<TR>
<TD vAlign=center align=center style="padding-top:3px" onClick="ClickPreview(); return false;">
<a name="lnkPreviewImg" id="lnkPreviewImg" href="Javascript:">
<img SRC="/_layouts/images/preview.jpg" NAME=ImgPreviewThumbnail ID=ImgPreviewThumbnail class=thumbnail height=90 width=120 alt="<SharePoint:EncodedLiteral runat='server' text='<%$Resources:wss,piclib_picturePreview%>' EncodeMethod='HtmlEncode' __designer:Preview="Picture Preview"/>"></a><br>
<a name="lnkPreviewTitle" id="lnkPreviewTitle" href="Javascript:" class="ms-imglibPreviewTitle">"<SharePoint:EncodedLiteral ID="EncodedLiteral2" runat='server' text='<%$Resources:wss,piclib_pictureFileName%>' EncodeMethod='HtmlEncode'/>"</a>
</TD>
</TR>
</TABLE>
Adding above code to content editor webpart.