It does not seems to be possible to convert InDesign's object libraries (.indl) to a JPEG picture, something that is probably tried by users that want to get a single picture listed in the library. You have to access the library from InDesign, find the piece you want to export and save it as a separate object.
Convert Adobe InDesign object library file to JPEG bitmap image format.
We have found 2 software records in our database eligible for .indl to .jpg file format conversion.
Microsoft Windows software - convert indl to jpg on Windows
Professional desktop document publishing software from Adobe
Convert from indl file format
The tables with software actions are a good pointer for what a certain program does with various file types and often may give users a good hint how to perform certain file conversion, for example the above-mentioned indl to jpg. However, it is not perfect and sometimes can show results which are not really usable because of how certain programs work with files and the possible conversion is thus actually not possible at all.
Apple macOS / Mac OS X software - convert indl to jpg on OS X
Mac version od Adobe's popular document designing and publishing software