I have gone through openclipart-0.18 and would suggest the following changes:

I would remove the following files because there exists dupplicates with
different names:
    animals/bugs/flying_wasp_gerald_g._02.png
    animals/mammals/bears/sleeping_bear_under_sta_03.png
    animals/mammals/dog_01_drawn_with_strai_03.png
    animals/mammals/dog_03_drawn_with_strai_02.png
    animals/mammals/dog_04_drawn_with_strai_02.png
    animals/mammals/dog_05_drawn_with_strai_02.png
    animals/mammals/dog_06_drawn_with_strai_02.png
    animals/mammals/dog_on_leash_gerald_g._02.png
    animals/mammals/horses/horse_1_konstantin_r._01.png
    computer/icons/battery_snuatautisticido_0[2-4].png
    education/scissors_03.png
    electronics/battery/battery_snuatautisticido_02.png
    electronics/battery/battery_snuatautisticido_03.png
    electronics/battery/battery_snuatautisticido_04.png
    food/beverages/flower-pot_02.png
    food/beverages/mug_toh_yen_cheng_02.png
    food/beverages/alcohol/martini_glass_k_yager_02.png
    office/scissors_02.png
    office/scissors_03.png
    people/elfish_girl_mo_.png
    people/jazz_enrique_meza_c_02.png
    people/man_head_mikhail_a.medve_01.png
    people/my_lovely_baby_enrique_m_02.png
    people/bodypart/left_foot_print_benji_pa_02.png
    people/bodypart/right_foot_print_benji_p_02.png
    plants/flowers/red_flower_03.png
    plants/trees/evergreen/christmas_tree_02.png
    recreation/music/fifties_jukebox_gerald_g_02.png
    recreation/music/jazz_enrique_meza_c_02.png
    recreation/music/war_drum_enrique_meza_c_02.png
    recreation/religion/creation_day_?_number_ge_0[2-4].png
    recreation/religion/discordian_sacred_chao_t_01.png
    recreation/sports/cronometro_mauro_olivo_0[2-3].png
    recreation/sports/table_tennis_racquets_o_01r.png
    signs_and_symbols/elder_sign_nubldoff_0[2-3]r.png
    signs_and_symbols/elder_sign_nurbldoff_0[1-6]r.png
    tools/ironing_board_gerald_g._02.png
    tools/scissors_03.png
    tools/vavuum_cleaner_-_uprigh_02.png
    tools/weapons/kallisti-grenade_2_nurbl_01.png


I would remove the following files because they are in a wrong subdirectory and
there exist duplicates in a good subdirecory:

    geography/eiffel_tower_michael_ja_r.png
    geography/shi_ken_01.png
    geography/symbol_for_a_church_on__01.png
    geography/war_drum_enrique_meza_c_0[1-2].png
    people/bodypart/fawn_mo_01.png
    recreation/art/airbrush_alejandro_tejad_.png
    recreation/games/cards/andalusia_01.png
    recreation/games/cards/jacob_leisler_mo_01.png
    signs_and_symbols/map_symbols/map_of_poland_guziec_.png
    shapes/airplane_nicu_buculei_01.png
    shapes/deer_matt_todd_01.png
    shapes/fancy_red_button_matt_to_01.png
    shapes/heart_jon_phillips_01.png
    shapes/left_foot_print_benji_pa_02.png
    shapes/right_foot_print_benji_p_02.png
    shapes/shield_matt_todd*.png
    shapes/wooden_mallot_benji_park_.png
    special/logaritmic_diagram_01.png
    special/examples
    special/patterns/model-view-controller_ia_01.png
    tools/compass_01.png


I would suggest to do the following movements because there are better
subdirectories for these pictures:

mv -v animals/birds/macchina_fotografica_di_01.png tools    
mv -v animals/lucchetto_grigio_archite_01.png tools    
mv -v animals/lucchetto_ottone_archite_01.png tools    
mv -v animals/fish/kallisti-grenade_1_nurbl_01.png tools/weapons    
mv -v computer/icons/yang_sergio_luiz_araujo__01.png signs_and_symbols    
mv -v geography/spyglass_vladimir_hernan_01.png tools    
mv -v plants/human_humain_umano_sed_r.png people    
mv -v recreation/games/cards/audio_cassette_mo_01.png electronics    
mv -v recreation/games/cards/brown_hair_boy_face_mike_02.png people    
mv -v recreation/games/cards/celtic-vine-corner_steve_01.png decorations    
mv -v recreation/*scuba_tank*.png tools    
mv -v shapes/cfbulb_*.png electronics/bulb    
mv -v shapes/clipart_by_nicu_buculei*.png signs_and_symbols/awards    
mv -v shapes/coke_*.png decorations    
mv -v shapes/fire-ball_benji_park_01.png signs_and_symbols    
mv -v shapes/forbici_e_pettine_sci_.png tools    
mv -v shapes/golden_hug_joel_montes_d_.png decorations    
mv -v shapes/gpride_jean_victor_balin_.png signs_and_symbols    
mv -v shapes/h_foot_print_jean_victor_.png signs_and_symbols    
mv -v shapes/orleans_express_*.png decorations    
mv -v shapes/shadow_babe_robert_seitz_01.png people    
mv -v shapes/stripper_jarno_vasamaa_01r.png people    
mv -v shapes/tangram_erwan_01.png people    
mv -v shapes/user_lambda_jean_victor_.png people    
mv -v shapes/arrows/reincarnate_nurbldoff_01r.png signs_and_symbols    
mv -v signs_and_symbols/led/led_rainbow_ganson.png electronics    
mv -v signs_and_symbols/led/leds_and_rainbow.png electronics    
mv -v signs_and_symbols/led shapes    


I am sorry that these list are based on the png files. I got them from a shell
script that cleans up the PNG version of the openclipart library for me. I could
generate .svg based lists on reguest.

BTW: The script is also able to remove some obvious and ugly duplicates
automatically. For example:

    - it deletes: transportation/turn_ahead.png
    - it keeps:   transportation/roadsigns/turn_ahead.png
  
It is because the second one is in more specific section and it does not make
sense to duplicate it in the parent directory.

If you are interested, I could create a list of these duplicates as well.


PS: Regarding the first group. Maybe, I do something wrong and I should get
different png files. Note that I compared the PNG files that were generated from
the SVG sources by the command:

     inkscape -f "$pict_svg" -e $OUTDIR/$PNGDIRNAME/clipart/$pict_dir/$pict_png"