Hello Fabrice and Eric, Thanks a lot for your suggestions. I ended up edebugging 'org-create-formula-image' to have a look at the created tex file (that is indeed cleaned up after the generation). The file was fine, but dvipng failed on it (with errors like "raw PostScriptdvipng warning: PostScript environment contains DVI commands dvipng warning: No image output from inclusion of raw PostScript"). I switched to imagemagick to do the conversion and everything now works.
The warnings were in the *Org Preview Latex Output* buffer, which I realized afterwards. However it's still tricky to debug because intermediate files are erased, so I could not initially run the command by hand to try to tweak it. Thanks again, Alan
