How very odd. You have stumbled up on a very peculiar little detail about Unicode. The odd part is that you are the second person in as many days to do that. Are you hosting this on a Mac?
What is going on is that you are using accented characters in your URLs and file names. There isn't anything wrong with that as long as you handle it properly. There are two ways to represent any accented character. The e with accent aigu, for example, can be represented as just the é character or as e´ with a combining mark in-between. If I use é to search for "Charest déchu", I will find it. But if I just search for "Charest dechu", I won't. Using the combining character (the decomposed form), allows either spelling to work. On a Mac, all files are stored using the decomposed form. On Linux, they seem to be stored differently.
On your server, the uploads directory lists all of your files (which is a bad idea by the way - you should turn off directory listings) and you can see how they are encoded. The problem is that there seems to be a mix of precomposed and decompsed Unicode.
For example,
the file t%c3%aate-fourmi.png is precomposed Unicode while
the file Charest-de%cc%81chu-polaroid.jpg is decomposed Unicode.
%c3%aa is UTF-8 for just the ê character
%cc%81 is UTF-8 for just the ´ combining character that modified the preceeding e.
You can use either one, but your URL must match how the file is actually encoded in the file system. I suggest not using any accents in file names so that your files are easily portable and easily referenced.