Images in upload folder with hexadecimal names

I’m using WordPress 3.4.1 with the Suffusion theme 4.3.0.

I’ve noticed that there are a large number of images with hexadecimal names, like 54f96e1d5f478186f66bde9d6aeda625.jpeg. I’m wondering how these images are being created, and what I can do to prevent their generation, as they don’t seem to be used by any post.

Testing the plugin provided in this Answer, I just saw that media_handle_sideload generates exactly this pattern, jpeg extension as well (instead of jpg).

Following its path through the core, it seems that only the filter wp_handle_upload could be used for dealing with that.

But a brief research shows an interesting use of wp_handle_upload_prefilter: Rename files during upload using variables.

A way of finding which element is using media_handle_sideload is:
– drop all the plugins and theme folders/files into a good editor (NotePad++, TextMate, etc) and do a global search for this filter.

After finding where it’s being called, a rename strategy can be thought of.

^{All this assuming the Sideload is responsible in OP’s case}