Is it possible to use the MySQL LIKE directive in an ElementCriteriaModel?
The * wildcard character should do the trick.

c.f. https://craftcms.com/docs/templating/elementcriteriamodel#parameter-value-syntax

$assets = craft()-&gt;elements-&gt;getCriteria(ElementType::Asset, array(
    'filename' =&gt; $prefix.'*',
    'limit' =&gt; null,
))-&gt;find();