The MIT licence only applies to the
software and associated documentation files
all together defined as the "Software" (in accordance with the US laws as well), and the copyright notice and the permission notice shall be included in all copies or substantial portions of the Software.
The definition of software may vary between countries due to different laws; however in the USA (I'm now referring to US laws as MIT is in the States) Software is legally defined as "Computer programs that comprise a series of instructions, rules, routines, or statements, regardless of the media in which recorded, that allow or cause a computer to perform a specific operation or series of operations", and associated documentation files. Only photos of the boards taken during design meetings are considered part of the Software and are covered by the Software license.
As those photos are artwork of an artist are not be considered software themselves.
I would update the README stating that your fork is using external resources that are not licensed under the MIT, inviting to double check the COPYING file for further information; and update the COPYING file as follow:
All of the photos of this project have been made available to this
project by John Doe and are copyrighted; any other use must be
authorized by the photographer which holds all the rights for those
Any other file of this project is available under the MIT license as follow:
Copyright [YEAR] [COPYRIGHT HOLDERS]
Permission is hereby granted, free of charge, to any person obtaining
a copy of this software and associated documentation files (the
"Software"), to deal in the Software without restriction, including
without limitation the rights to use, copy, modify, merge, publish,
distribute, sublicense, and/or sell copies of the Software, and to
permit persons to whom the Software is furnished to do so, subject to
the following conditions:
The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.