One transparent pixel as <a href="https://en.wikipedia.org/wiki/Graphics_Interchange_Format" class="extiw" title="en:Graphics Interchange Format">GIF</a>, 45 bytes without <a href="https://en.wikipedia.org/wiki/Lempel-Ziv-Welch" class="extiw" title="en:Lempel-Ziv-Welch">LZW</a> compression. As of 2014 <a href="https://en.wikipedia.org/wiki/commons:Category:Transparent_pixels" class="extiw" title="w:commons:Category:Transparent pixels">commons</a> offered three different LZW pixels (two 42 bytes and one 43 bytes), and now also this with <a href="https://en.wikipedia.org/wiki/MD5" class="extiw" title="en:MD5">MD5</a>: 9323cda5 b644259f e90fd862 5c7e66c9. Meanwhile the LZW <a href="https://en.wikipedia.org/wiki/software_patent#Unisys_case" class="extiw" title="en:software patent">software patents</a> expired.
<a href="//commons.wikimedia.org/wiki/User:Be..anyone" title="User:Be..anyone">Be..anyone</a>
Own work  using: well-known 43 bytes LZW, MD5: fc94fb0c 3ed8a8f9 09dbc763 0a0987ff