  We have developed a new ISOCAM data reduction technique based on wavelet
analysis, especially designed for the detection of faint sources in
mid-infrared surveys. This method, the Pattern REcognition Technique for Isocam
data (PRETI) has been used to reduce the observations of the Hubble Deep Field
(HDF) and flanking fields with ISOCAM at 6.75 (LW2) and 15 microns (LW3).
Simulations of ISOCAM data allow us to test the photometric accuracy and
completeness of the reduction. We detect 49 objects in the ISO-HDF at high
confidence level, 42 in the LW3 filter, 3 in the LW2 filter, and 4 in both
filters. An additional, less secure, list of 100 sources is presented, of which
89 are detected at 15 microns only, 7 at 6.75 microns only and 4 in both
filters. Number counts derived from our results show an excess by a factor of
10 with respect to the prediction of a no evolution model (Franceschini 1998)
in the LW3 band. On the contrary, the number of sources in the LW2 band is
compatible with the prediction of such a model, but with greater uncertainties,
given the small number of detections.
