PHP Operators, how do I make the code shorter? : Original code:

    if(mimeType == 'image/jpeg' or mimeType == 'image/png' or mimeType == 'image/gif' && filename)

I tried this, but it will include unwanted *pdf.

    if (mimeType == ('image/jpeg' ||'image/png' ||'image/gif') && $part->filename)

 How do I make the code shorter ? Thank you.