The `Image Resizer` TBB should have a Parameters Schema set, this Schema has 4 fields

- Width, the resize width
- Height, the resize height
- Percentage, optional resize percentage
- ItemName, resize only items named like this

If you are missing that, you should be able to create it based on the following source, and attach that to your TBB so you can specify what you need in the Template Builder:

<!-- language: lang-xml -->

    <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" xmlns="uuid:1D7B0405-BE6C-4DC3-8B6D-36D52C41EA8F" xmlns:tcmi="http://www.tridion.com/ContentManager/5.0/Instance" elementFormDefault="qualified" targetNamespace="uuid:1D7B0405-BE6C-4DC3-8B6D-36D52C41EA8F">
      <xsd:import namespace="http://www.tridion.com/ContentManager/5.0/Instance" schemaLocation="cm_xml_inst.xsd"></xsd:import>
      <xsd:annotation>
        <xsd:appinfo>
          <tcm:Labels xmlns:tcm="http://www.tridion.com/ContentManager/5.0">
            <tcm:Label ElementName="Width" Metadata="false">Resize width</tcm:Label>
            <tcm:Label ElementName="Height" Metadata="false">Resize height</tcm:Label>
            <tcm:Label ElementName="Percentage" Metadata="false">Resize percentage</tcm:Label>
            <tcm:Label ElementName="ItemName" Metadata="false">Resize only item named</tcm:Label>
          </tcm:Labels>
        </xsd:appinfo>
      </xsd:annotation>
      <xsd:element name="Parameters">
        <xsd:complexType>
          <xsd:sequence>
            <xsd:element name="Width" minOccurs="0" maxOccurs="1" type="xsd:decimal">
              <xsd:annotation>
                <xsd:appinfo>
                  <tcm:CustomURL xmlns:tcm="http://www.tridion.com/ContentManager/5.0">/TemplateBuilder/TemplateParameterDescriptions/ImageResizer.html#Width</tcm:CustomURL>
                  <tcm:ExtensionXml xmlns:tcm="http://www.tridion.com/ContentManager/5.0"></tcm:ExtensionXml>
                </xsd:appinfo>
              </xsd:annotation>
            </xsd:element>
            <xsd:element name="Height" minOccurs="0" maxOccurs="1" type="xsd:decimal">
              <xsd:annotation>
                <xsd:appinfo>
                  <tcm:CustomURL xmlns:tcm="http://www.tridion.com/ContentManager/5.0">/TemplateBuilder/TemplateParameterDescriptions/ImageResizer.html#Height</tcm:CustomURL>
                  <tcm:ExtensionXml xmlns:tcm="http://www.tridion.com/ContentManager/5.0"></tcm:ExtensionXml>
                </xsd:appinfo>
              </xsd:annotation>
            </xsd:element>
            <xsd:element name="Percentage" minOccurs="0" maxOccurs="1" type="xsd:decimal">
              <xsd:annotation>
                <xsd:appinfo>
                  <tcm:CustomURL xmlns:tcm="http://www.tridion.com/ContentManager/5.0">/TemplateBuilder/TemplateParameterDescriptions/ImageResizer.html#Percentage</tcm:CustomURL>
                  <tcm:ExtensionXml xmlns:tcm="http://www.tridion.com/ContentManager/5.0"></tcm:ExtensionXml>
                </xsd:appinfo>
              </xsd:annotation>
            </xsd:element>
            <xsd:element name="ItemName" minOccurs="0" maxOccurs="1" type="xsd:normalizedString">
              <xsd:annotation>
                <xsd:appinfo>
                  <tcm:CustomURL xmlns:tcm="http://www.tridion.com/ContentManager/5.0">/TemplateBuilder/TemplateParameterDescriptions/ImageResizer.html#ItemName</tcm:CustomURL>
                  <tcm:ExtensionXml xmlns:tcm="http://www.tridion.com/ContentManager/5.0"></tcm:ExtensionXml>
                </xsd:appinfo>
              </xsd:annotation>
            </xsd:element>
          </xsd:sequence>
        </xsd:complexType>
      </xsd:element>
    </xsd:schema>