Primary Syphilis

Two erythematous, painless round chancres on penis. Source: DermNet (https://dermnetnz.org/topics/syphilis-images) Creative Commons Attribution-NonCommercial-NoDerivs 3.0 (New Zealand)

Scabies

Small crusted papules, eczematous plaques, intense pruritus and excoriations, and superficial linear burrows.

Meningococcemia

Hemorrhagic papules or petechia with purpuric centres in acral distribution. (Courtesy of The Hospital for Sick Children Slide Library, Toronto)