The design of the text box filter/input is to just replace the value entered in the text box to the place where it's token is referenced. So, if your search is ... | search positive_sentence="*$yourtextboxtoken$*" , then, if you enter picture, the search will be become ... | search positive_sentence="*picture*" and for picture OR pic, it will be ... | search positive_sentence="*picture OR pic*".
If you're looking for a custom interpretation/transformation of text box values, you'd need to write your SPL accordingly. E.g. if you want picture OR pic to be translated as ... | search positive_sentence="*picture*" OR positive_sentence="*pic*", then something like this would work
your base search | search [| gentimes start=-1 | eval search="positive_sentence=\"*".replace("$yourtextboxtoken$","(\s+(OR|AND)\s+)","*\"\1positive_sentence=\"*")."*\"" | table search]